Influence of gestational age and fetal heart rate on the fetal mechanical PR interval.

OBJECTIVE: The fetal mechanical PR interval obtained via pulsed Doppler has previously been demonstrated to correlate with electrocardiographic PR interval measured in the neonate. We sought to further analyze the influence of fetal heart rate and gestational age upon the fetal mechanical PR interval. METHODS: We searched our database for mechanical PR intervals, which were obtained during fetal echocardiography performed in our antenatal diagnostic unit. We included fetuses with a normal cardiac structural survey. The mechanical PR interval is measured from the A wave of the mitral valve to the beginning of ventricular systole corresponding to the opening of the aortic valve. Linear regression curves were generated to examine the correlation of mechanical PR interval with gestational age and fetal heart rate. Analysis of variance was used to compare the mean variation across three gestational age groups: 17-21.9 weeks (n = 24), 22-25.9 weeks (n = 52) and 26-38 weeks (n = 20). RESULTS: Mechanical PR intervals were measured in 96 fetuses with normal fetal echocardiography. The mechanical PR interval was 123.9 +/- 10.3 ms (mean +/- SD), with a range of 90-150 ms. Linear regression curves correlating mechanical PR interval with fetal heart rate and gestational age demonstrated a flat slope with R2 = 0.016, p = 0.22 and R2 = 0.0004, p = 0.85, respectively. The mechanical PR interval measured over the three gestational ages was as follows (mean +/- SD): 122.3 +/- 10.5 ms for 17-21.9 weeks; 125.0 +/- 9.6 ms for 22-25.9 weeks; and 123.1 +/- 11.9 ms for 26-38 weeks. Analysis of variance revealed no difference among the mechanical PR interval means measured over the three gestational age groups (p = 0.53). CONCLUSIONS: Fetal mechanical PR interval ranges from 90 to 150 ms in fetuses with sonographically normal fetal cardiac structure and rate. The mechanical PR interval appears to be independent of gestational age and fetal heart rate.     

Improvements in the registration and analysis of fetal heart rate records at the bedside

A microprocessor system is described for on-line analysis of the fetal heart rate detected by conventional Doppler systems. A brief account is given of the instrumentation and program structure. The system has been tested by analysing normal and abnormal antenatal fetal heart rate records. Pulse Doppler with autocorrelation measurement of the fetal pulse interval reduced the signal loss in clinical practice by a factor of 10, to an average of 2.1% in 629 records from uncomplicated pregnancies. Yet it is still necessary to identify signal loss, because it occasionally rises to unacceptable levels in association with fetal movements or hiccups. Medium-term measures of fetal heart rate variation (within 16-0.1 cycles/min) varied with gestational age, but were a better index of fetal well-being than longer-term measures. The application of the system to fetal monitoring is illustrated.     

Improvements in the registration and analysis of fetal heart rate records at the bedside

Summary. A microprocessor system is described for on-line analysis of the fetal heart rate detected by conventional Doppler systems. A brief account is given of the instrumentation and program structure. The system has been tested by analysing normal and abnormal antenatal fetal heart rate records. Pulse Doppler with autocorrelation measurement of the fetal pulse interval reduced the signal loss in clinical practice by a factor of 10, to an average of 2.1% in 629 records from uncomplicated pregnancies. Yet it is still necessary to identify signal loss, because it occasionally rises t o unacceptable levels in association with fetal movements or hiccups. Medium-term measures of fetal heart rate variation (within 16–0.1 cycles/min) varied with gestational age, but were a better index of fetal well-being than longer-term measures. The application of the system t o fetal monitoring is illustrated.     

Pattern of the normal human fetal heart rate

With an improved method for fitting baselines to human fetal heart-rate traces, the patterns of episodic variations, accelerations and decelerations were similar in 215 64-min records from normal pregnancies and in 95 with mild hypertension and normal outcome. The change in signal loss with gestational age, by Doppler ultrasound for recording heart rate, was entirely due to the greater loss in episodes of high heart-rate variation. The changes in the numbers and sizes of accelerations and decelerations with gestational age were described. There were many records which had only one or no acceleration at 28-33 weeks gestation (16.2%) or 34-41 weeks (7.3%). However, only two (0.7%) had episodes of high heart-rate variation lasting less than 10 min from 28 weeks onwards. The presence of these episodes, with clusters of fetal movements, is therefore likely to be a better numerical index of normality.     

Pattern of the normal human fetal heart rate

Summary. With an improved method for fitting baselines to human fetal heart-rate traces, the patterns of episodic variations, accelerations and decelerations were similar in 215 64-min records from normal pregnancies and in 95 with mild hypertension and normal outcome. The change in signal loss with gestational age, by Doppler ultrasound for recording heart rate, was entirely due to the greater loss in episodes of high heart-rate variation. The changes in the numbers and sizes of accelerations and decelerations with gestational age were described. There were many records which had only one or no acceleration at 28–33 weeks gestation (16.2%) or 34–41 weeks (7.3%). However, only two (0.7%) had episodes of high heart-rate variation lasting <10 min from 28 weeks onwards. The presence of these episodes, with clusters of fetal movements, is therefore likely to be a better numerical index of normality.     

Influence of gestational age and fetal heart rate on the fetal mechanical PR interval

Objective: The fetal mechanical PR interval obtained via pulsed Doppler has previously been demonstrated to correlate with electrocardiographic PR interval measured in the neonate. We sought to further analyze the influence of fetal heart rate and gestational age upon the fetal mechanical PR interval.

Methods: We searched our database for mechanical PR intervals, which were obtained during fetal echocardiography performed in our antenatal diagnostic unit. We included fetuses with a normal cardiac structural survey. The mechanical PR interval is measured from the A wave of the mitral valve to the beginning of ventricular systole corresponding to the opening of the aortic valve. Linear regression curves were generated to examine the correlation of mechanical PR interval with gestational age and fetal heart rate. Analysis of variance was used to compare the mean variation across three gestational age groups: 17–21.9 weeks (n?=?24), 22–25.9 weeks (n?=?52) and 26–38 weeks (n?=?20).

Results: Mechanical PR intervals were measured in 96 fetuses with normal fetal echocardiography. The mechanical PR interval was 123.9?±?10.3?ms (mean?±?SD), with a range of 90–150?ms. Linear regression curves correlating mechanical PR interval with fetal heart rate and gestational age demonstrated a flat slope with R²?=?0.016, p?=?0.22 and R²?=?0.0004, p?=?0.85, respectively. The mechanical PR interval measured over the three gestational ages was as follows (mean?±?SD): 122.3?±?10.5?ms for 17–21.9 weeks; 125.0?±?9.6?ms for 22–25.9 weeks; and 123.1?±?11.9?ms for 26–38 weeks. Analysis of variance revealed no difference among the mechanical PR interval means measured over the three gestational age groups (p?=?0.53).

Conclusions: Fetal mechanical PR interval ranges from 90 to 150?ms in fetuses with sonographically normal fetal cardiac structure and rate. The mechanical PR interval appears to be independent of gestational age and fetal heart rate.     

Low human fetal heart rate variation in normal pregnancy

The fetal heart rates of 340 normal singleton pregnancies at 30-33 weeks gestation were screened using a microprocessor system on-line. Eleven fetuses (3.2%) with a heart rate variation less than the 5th centile were identified, of whom 10 were studied longitudinally. At 30-33 weeks the mean minute range of pulse intervals (a measure of fetal heart rate variation) was 31.4 (SE 1.5) ms compared with 51.0 (SE 3.4) ms in a randomly selected control group. The study group continued to have significantly lower fetal heart rate variation than controls on each of three subsequent occasions until delivery. There were no significant differences between the two groups in fetal outcome, which was good. This demonstrates that a small proportion of normal fetuses have consistently low heart rate variation, and helps to define the lower limit of the normal distribution of fetal heart rate variation. After delivery, there were no significant differences between heart rate or its variation between the two groups. We conclude that the lower prenatal heart rate variation in the study group was a consequence of the uterine environment.     

Antenatal fetal heart rate variation in relation to the respiratory and metabolic status of the compromised human fetus

Three groups of women were delivered by caesarean section before labour: for an abnormal fetal heart rate (FHR) trace (21 cases, group 1), or for maternal deterioration in severe pre-eclampsia without gross fetal heart rate abnormalities (20 cases, group 2), or to avoid mechanical difficulties in labour at term (30 cases, group 3). The mean gestational ages of the first two groups were 32 weeks with a high proportion of infants small-for-gestational-age. In group 1, FHR variation (mean range of pulse intervals) was less than half (20.6 SE 1.2 ms) of the normal value at the same age (44.4 SE 1.5 ms). This was associated with hypoxaemia (mean umbilical artery PO2 of 6 mmHg at delivery), with evidence of compensation shown by an elevated amniotic fluid erythropoietin. The fetuses were hypoglycaemic and had greater umbilical artery blood alanine concentrations, but no large changes in adenine nucleotide or endorphin plasma concentrations. Although there was a minor degree of respiratory acidaemia at birth, there was not significant metabolic acidaemia. The results demonstrate that the reduced variation of 'suboptimal' and 'decelerative' fetal heart rate records is associated with fetal hypoxaemia and evidence of nutritional deprivation, but not with asphyxia.     

Fetal deaths in the United States. Influence of high-risk conditions and implications for management

OBJECTIVE: To estimate the effect of specific maternal-fetal high-risk conditions on the risk and timing of fetal death. METHODS: This study examined 10,614,679 non-anomalous singleton pregnancies delivering at or beyond 24 weeks' gestation, derived from the U.S. linked birth/infant death data sets, 1995-1997. Fetal death rates for pregnancies at low risk were compared with pregnancies complicated by chronic hypertension, gestational hypertensive disorders, diabetes, small for gestational age infants, and abruption. Adjusted relative risks as well as population-attributable risks for fetal death were derived by gestational age for each high-risk condition compared with low-risk pregnancies. RESULTS: The fetal death rate for low-risk pregnancies was 1.6 per 1000 births. Adjusted relative risk for fetal death was 9.2 (95% confidence interval [CI] 8.8, 9.7) for abruption, 7.0 (95% CI 6.8, 7.2) for small for gestational age infants, 1.4 (95% CI 1.3, 1.5) for gestational hypertensive disorders, 2.7 (95% CI 2.4, 3.0) for chronic hypertension, and 2.5 (95% CI 2.3, 2.7) for diabetes. Fetal death rates were lowest between 38 and 41 weeks. The fetal death rate (per 1000 births) for these high-risk conditions was 61.4, 9.6, 3.5, 7.6, and 3.9, respectively. Almost two thirds of fetal deaths were attributable to the pregnancy complications examined. CONCLUSION: High-risk conditions in pregnancy are associated with an increased risk for fetal death, particularly in the third trimester. Delivery should be considered at 38 weeks, but no later than 41 weeks, for these pregnancies.     

Short-term variation in abnormal antenatal fetal heart rate records

In a retrospective study the relation of reduced fetal heart rate variation to fetal acidemia was analyzed with a computerized system for numeric analysis. Between 1983 and 1987, 78 pregnancies were identified in which at least one record of the fetal heart rate had very low long-term variation. The outcome was analyzed to determine the numeric criteria of fetal heart rate variation that most efficiently detect a fetus that will die (preterminal) or is dying (terminal). Because fetal compromise was found on occasion to be associated with a slow sinusoidal fetal heart rate rhythm that increased measures of long-term variation. It was necessary to define a new index of short-term fetal heart rate variation (the 1/16 minute epoch-epoch variation). This was closely related to long-term variation (r = 0.9) but provided better detection of preterminal records as judged by metabolic acidemia at delivery or intrauterine death.     

Antenatal fetal heart rate variation in relation to the respiratory and metabolic status of the compromised human fetus

Summary. Three groups of women were delivered by caesarean section before labour: for an abnormal fetal heart rate (FHR) trace (21 cases, group 1), or for maternal deterioration in severe pre-eclampsia without gross fetal heart rate abnormalities (20 cases, group 2), or to avoid mechanical difficulties in labour at term (30 cases, group 3). The mean gestational ages of the first two groups were 32 weeks with a high proportion of infants small-for-gestational-age. In group 1, FHR variation (mean range of pulse intervals) was less than half (20·6 SE 1·2 ms) of the normal value at the same age (44·4 SE 1·5 ms). This was associated with hypoxaemia (mean umbilical artery P o₂ of 6 mmHg at delivery), with evidence of compensation shown by an elevated amniotic fluid erythropoietin. The fetuses were hypoglycaemic and had greater umbilical artery blood alanine concentrations, but no large changes in adenine nucleotide or endorphin plasma concentrations. Although there was a minor degree of respiratory acidaemia at birth, there was not significant metabolic acidaemia. The results demonstrate that the reduced variation of 'suboptimal' and 'decelerative' fetal heart rate records is associated with fetal hypoxaemia and evidence of nutritional deprivation, but not with asphyxia.     

Contraction Stress Fetal Heart Rate Monitoring at Preterm Gestational Ages

The evaluation of fetal well-being by fetal heart rate monitoring at preterm gestational ages remains a difficult and important area for investigation. While the nonstress test has achieved widespread usage, a role for the contraction stress test remains uncertain. This study describes the outcome of 113 contraction stress tests which were performed for persistent fetal heart rate nonreactivity in 78 pregnancies of less than 37 completed weeks' gestation. There were no fetal deaths and no obstetric complications which could be attributed to these tests. The finding of a negative contraction stress test provided reassurance which facilitated significant prolongation of pregnancy. Contraction stress test appear to be a safe and effective method of investigating further the clinical dilemma of persistent fetal heart rate nonreactivity in high risk pregnancies at preterm gestational ages.     

Studies on features of fetal movement and development of human fetus with use of fetal actogram

In 167 normal fetuses at 26 to 41 weeks of gestation, features of fetal movement and fetal development were investigated with use of actocardiograph in connection with a microcomputer system. The signals of fetal movement obtained by actocardiograph were stored in a floppy disc every 250 ms for 5 minutes through an AD-converter, and were analyzed every 5 minutes with the computer to reveal 3-dimensional (3-D) histograms. The 3-D histogram of fetal movement was composed of number, amplitude and interval of the signals in 11 voltage steps between 0.05 and 0.55V. The histogram clearly indicated state of fetal behavior, being either resting or active state. Fetal movement such as rolling movement, breathing movement and hiccup could be also identified with the computer analysis. In 68 normal fetuses at 14 to 41 weeks of gestation, the cross-correlation between fetal movement and fetal heart rate (FHR) were examined with the computer analysis. Finally fetal responses to acoustic and light stimulation were evaluated with use of pure-tone generator and flashlight. Acoustic stimulation was carried out in 53 normal fetuses at 28 to 41 weeks and light stimulation was performed in 116 normal fetuses at 18 to 41 weeks of gestation. The fetal responses were evaluated with actocardiogram. As a result, 1) Frequency in active state decreased and resting state increased as gestational weeks advanced, and then the frequencies of both state remained constant after 37 weeks of gestation. Duration of resting state also increased from 26 weeks to 37 weeks. These observations may suggest that fetal behavior can be established by 37 weeks of gestation. 2) Frequency in rolling movement decreased until 37 weeks of gestation, and then the movement increased during 38-41 weeks. Frequency in breathing movement increased to 33 weeks of gestation, then it remained constant. Hiccup occurred most frequently at 30-33 weeks, and it decreased thereafter. The function in fetal respiratory movement may be accomplished by 33 weeks of gestation. 3) Positive cross-correlation between fetal movement and FHR was observed as gestational weeks advanced. The correlation coefficient increased from 14 weeks up to 41 weeks. Acceleration of FHR following fetal movement eventually occurred in fetuses at 16 weeks, but the onset of acceleration delayed than normally occurred in developed fetuses. The delay was shortened in fetuses at 24 weeks and this was comparable to the delay in developed fetuses. These results suggest that the linkage of the acceleration of FHR with fetal movement is established at 24 weeks of gestation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Second-trimester fetal monitoring and preterm delivery in pregnancies with systemic lupus erythematosus and/or circulating anticoagulant

Antepartum fetal monitoring was initiated at 19 to 26 weeks' gestation in 15 pregnancies: six (five with systemic lupus erythematosus, one with circulating anticoagulant) with a complicated antepartum course (group 1); three, all systemic lupus erythematosus, with a normal antepartum course (group 2); and six normal control pregnancies (group 3). Group 1 all exhibited nonperiodic fetal heart rate decelerations, without the classical appearance of early, late, or variable decelerations, and four of the six had fetal bradycardia. In three group 1 cases, there was no active intervention because of early gestational age, and fetal death occurred at 23, 27, and 27 weeks, respectively. The other three patients in group 1 received betamethasone and were delivered by cesarean section at 28 to 30 weeks. There were no cases of respiratory distress syndrome or neonatal death. Five of the six infants in group 1 were small for gestational age. The nonperiodic fetal heart rate decelerations were absent in both groups 2 and 3 who all had normal fetal outcomes at term. The abnormal finding of women with nonperiodic fetal heart rate decelerations at 20 to 28 weeks may detect the fetus at risk for intrauterine death in pregnancies complicated by systemic lupus erythematosus or circulating anticoagulant. Continued surveillance, steroid induction of lung maturity, and delivery should be considered in these cases.     

Limitations of antenatal fetal heart rate monitors

Erroneous or doubtful decelerations in fetal heart traces were present in 111 of 1000 consecutive antenatal clinical records obtained by monitors with autocorrelation. The incidence was 20% in fetuses less than 30 weeks of gestational age. Their elimination reduced the number of "decelerative" records by 42%. Erroneous or doubtful accelerations were also present in 11% of records. These errors are caused by the fetal heart rate monitor and may contribute to the high intraobserver and interobserver variation on visual analysis. They can be detected by computer analysis.     

Predicting concordance of biochemical lung maturity in the preterm twin gestation

Objective: To determine the occurrence of maternal and fetal complications in low-risk pregnancies beyond 39 weeks and to re-evaluate the acceptable cut-off (42 weeks) for induction of labor. Study design: A total of 36 160 low-risk pregnancies with reliable dating of gestational age (last menstrual period and early ultrasound examination) were evaluated retrospectively for fetal and maternal complications, including non-progressive labor, cervical tear, retained placenta, postpartum hemorrhage, vacuum delivery, Cesarean section, macrosomia, meconium-stained amniotic fluid, non-reassuring fetal heart rate monitoring and ante-, intra- and postpartum death. Pregnancy outcomes at different gestational ages were compared using univariate and multivariate analysis and receiver operator curves. Results: The rates of non-progressive labor stage I and II, retained placenta, vacuum delivery, Cesarean section, macrosomia, meconium-stained amniotic fluid and non-reassuring fetal heart rate monitoring were found to be significantly higher with increasing gestational age in the univariate analysis. These parameters were evaluated using multivariate analysis and the following were found to be significantly higher: non-progressive labor stage I and II, macrosomia, meconium-stained amniotic fluid and Cesarean section. Statistical analysis (receiver operator curves) showed that the most significant rise in the risk for non-progressive labor occurred after 42 completed weeks of gestation, and after 41 completed weeks for macrosomia, meconium-stained amniotic fluid and Cesarean section. Conclusions: The rates of non-progressive labor stage I and II, meconium-stained amniotic fluid, macrosomia and Cesarean section were significantly higher with increasing gestational age. In order to decrease the rate of macrosomia, meconium-stained amniotic fluid and Cesarean section, we suggest that induction of labor should be considered before 42 weeks.     

Computerized measurement of heart rate variation in fetal anemia caused by rhesus alloimmunization.

OBJECTIVE: The purpose of this study was to examine the relationship between fetal heart rate variation and fetal hematocrit. STUDY DESIGN: In 36 red-cell alloimmunized pregnancies (mean gestational age 30, range 25 to 36 weeks) 65 computerized fetal heart rate recordings were obtained before ultrasonographically guided fetal blood sampling for the measurement of fetal hematocrit. The recordings were captured and analyzed by a microcomputer on-line. Fetal heart rate variation in anemic fetuses was accurately measured. RESULTS: Significant positive correlations between short-term or long-term heart rate variation and fetal hematocrit have been demonstrated even after adjusting for the effect of gestation (r = 0.60, n = 65, p less than 0.01, y = 19.264 + 0.913x - 0.003x2; r = 0.52, n = 65, p less than 0.01, y = 21.13 + 0.858x - 0.003x2, respectively). The relationship was best described by a quadratic model. When short-term variation was less than 5 milliseconds or long-term variation was less than 30 milliseconds, the positive predictive values for fetal hematocrit of less than 30 were 85% and 90%, and the negative predictive values 56% and 57%, respectively. CONCLUSION: Computerized recording and analysis of fetal heart rate variation may prove to be a useful noninvasive tool for assessing fetal anemia in red-cell alloimmunization.     

Phase-rectified signal averaging as a new method for surveillance of growth restricted fetuses

Objective: This study aims to compare average acceleration capacity (AAC), a new parameter to assess the dynamic capacity of the fetal autonomous nervous system, and short term variation (STV) in fetuses affected by intrauterine growth restriction (IUGR) and healthy fetuses. Methods: A prospective observational study was performed, including 39 women with IUGR singleton pregnancies (estimated fetal weight <10th percentile and umbilical artery resistance index >95th percentile) and 43 healthy control pregnancies matched according to gestational age at recording. Ultrasound biometries and Doppler examination were performed for identification of IUGR and control fetuses, with subsequent analysis of fetal heart rate, resulting in STV and AAC. Follow-up for IUGR and control pregnancies was done, with perinatal outcome variables recorded. Results: AAC [IUGR mean value 2.0 bpm (interquartile range = 1.6–2.1), control 2.7 bpm (2.6–3.0)] differentiates better than STV [IUGR 7.4?ms (5.3–8.9), control 10.9?ms (9.2–12.7)] between IUGR and control. The area under the curve for AAC is 97 % [95% CI = (0.95–1.0)], for STV 85 % (CI = 0.76–0.93; p < 0.01). Positive predictive value for STV is 77% and negative predictive value is 81%. For AAC both positive and negative predictive values are 90%. Conclusions: AAC shows an improvement to discriminate between normal and compromised fetuses at a single moment in time, in comparison with STV.     

Premature rupture of membranes before 32 weeks of gestation: prenatal prognosis factors

OBJECTIVE: Premature preterm rupture of membranes (PPROM) accounts for a significant part of overall perinatal mortality and morbidity. This study aims to define potential prognostic factors for neonatal outcome. PATIENTS AND METHODS: One hundred and thirty-one pregnancies complicated with PPROM at between 26 and 32 weeks were retrospectively reviewed over a three-year period. The influence of chorioamnionitis on perinatal morbidity and mortality was assessed using a composite outcome. RESULTS: On admission, gestational age (GA) at diagnosis, fetal heart rate anomalies and increasing severity of clinical features of chorioamnionitis were significantly related with an adverse outcome. Significant factors associated with a favourable outcome were an administration of steroids for lung maturation, prophylactic antibiotics and tocolytic therapies. Stratifying according to GA at PPROM, the survival rates were 43 and 52% at before 22 weeks and between 22 and 26 weeks respectively. The prognosis dramatically improved after 26 weeks with an 84.6% rate of survival without impairment. Although this rate reached 97.5% after 30 weeks, there was no statistical evidence supporting any benefit to prolong pregnancies beyond this point. The complete expression of chorioamnionitis independently increased the mortality rate by 41% (OR=1.41; 95% CI [0.99-2.01]. Overall, the most relevant factor was GA at delivery, levelling the prognostic value of GA at diagnosis. DISCUSSION AND CONCLUSION: If no consensus rules PPROM at the moment, the most efficient prognosis factor before 34 weeks is mostly determined by GA at delivery.     

Male gender predisposes to prolongation of pregnancy

OBJECTIVE: The purpose of this study was to evaluate the association between fetal gender and prolonged pregnancy. STUDY DESIGN: All deliveries in Sweden between 1987 and 1996 were evaluated for participation in this study. Inclusion criteria included (1) singleton pregnancy, (2) the absence of apparent congenital or chromosomal anomalies, (3) accurate dating established by early second trimester ultrasound examination, and (4) gestational age at delivery of > or =37 weeks (ie, > or =259 days). Initially, we calculated the mean gestational age at delivery and the percentage of prolonged pregnancies by fetal gender. Subsequently, the Mantel-Haenszel chi-square analysis was used to calculate the weekly odds ratios and their corresponding 95% confidence intervals for the delivery of a male fetus beyond 37 weeks of gestation. RESULTS: The study population comprised 656,423 deliveries; 333,192 were male deliveries, and 323,231 were female deliveries (male/female ratio, 1.03). The mean gestational age at delivery was significantly higher in male fetuses (280.6 +/- 8.9 days vs 279.8 +/- 8.6 days, respectively; P <.0001). The percentage of pregnancies that delivered beyond term was significantly higher for male relative to female fetuses (26.5% vs 22.5% [P <.000001] at > or =41 weeks of gestation and 7.6% vs 5.5% [P <.000001] at > or =42 weeks of gestation, respectively). The weekly odds ratios for a delivery of a male fetus beyond term were 1.14, 1.39, and 1.50 at 41, 42, and 43 weeks, respectively. CONCLUSION: Male gender significantly predisposes to the prolongation of pregnancy to the extent that, by 43 weeks of gestation, there are 3 male deliveries for every 2 female deliveries.