A method for objective measurement of fetal head compression during the second stage of labor

The article describes a novel method for the objective measurement of compression forces to which the fetal head is exposed during labor. This involves the placement of a transducer, housed in a silicone rubber and brass casing (18 mm diameter, 6.5 mm thick), over the parietal bone area. The compression forces monitored with the transducer in this position provide an estimate of the intracranial pressure. The technique thus not only provides a means of assessing fetal head compression, but also the efficacy of the expulsion efforts of the mother. Pressure recordings taken during the second stage of 24 deliveries revealed a marked variation in the magnitude of the compression forces between the births.     

Intrapartum sonographic signs: new diagnostic tools in malposition and malrotation

In the past years, numerous studies have been published on the use of ultrasound during labor, showing this is an effective, accurate and objective tool for the assessment of the fetal head position and station. Literature affirmed that traditional transvaginal digital examination is highly subjective and dependent on the operator’s experience. On the contrary, the use of intrapartum suprapubic transabdominal ultrasound can improve accuracy in determination of fetal head position and the precise knowledge of the location of specific fetal head landmarks in relationship to maternal pelvis. Intrapartum ultrasound will assist obstetricians in the diagnosis of normal labor progression, suggesting when medical and or operative intervention should be taken in case of complications. During each fetal head movement, there is a very specific relationship between fetal head landmarks and well-identified maternal structures, so the ultrasound diagnosis is performed step by step. In this review, we summarized the clinical situation of the fetal head in the pelvis and the relative ultrasonographic signs. Moreover, we collected all the ultrasonographic measures to diagnose the fetal head progression and rotations in the birth canal.     

Fetal foot length--a new parameter for assessment of gestational age

Ultrasonographic measurement of fetal foot length, a new parameter, was correlated with the gestation age. One hundred and five ultrasonographic measurement of fetal foot length was performed between 13 and 42 weeks gestation. Comparison of linear regression of foot length versus gestational age demonstrated a strong correlation with an r2 value of 0.84 (P less than 0.001). Ninety-five percent confidence intervals at each week compared favorably with both biparietal diameter and femur length data. Mean foot lengths at each week of gestation compared favorably with data based on pathological specimens described in 1920 (Streeter GL: Weight, sitting height, head size, foot length and menstrual age of the human embryo. Contrib Embryol Carnegie Inst. 11: 143, 1920). Measurement of fetal foot length is of particular use when other parameters do not accurately predict gestational age, e.g. hydrocephalus, anencephaly, short limb dysplasia. It can also be used in conjunction with biparietal diameter and femur length in the management of patients with premature labor in order to patients with premature labor in order to accurately predict gestational age. Hence the present study demonstrates that the ultrasonographic measurement of foot length is a reliable indicator of gestational age.     

Evaluation of cephalometry by ultrasound in breech presentation

Previous reports on the ultrasonographic measurement of the biparietal diameter of the fetal head have presented too few cases to establish the method's value when the head is in the fundus of the uterus. Fifty fetal head mensurations in breech presentation were compared to measurements obtained by postpartum ultrasound and calipers and were found to be accurate within the limits of previous investigators.     

Effects of experimental head compression on transcutaneous scalp PO2 in fetal lambs

Equatorial compression of the fetal head is known to occur during labor; its effect on trancutaneous scalp PO2 (PtCO2) was investigated in acute experiments in four fetal lambs. Fetal PtCO2, and oxygen tension (PaO2) and flow in a carotid artery were continuously measured. Equatorial head compression was obtained by inflating a cuff around the fetal head. A strong relationship was shown to exist between PtCO2 and PaO2 values in the normoxemic and hypoxemic fetus. Stepwise compression of the fetal head resulted in a PtCO2 of zero at cuff pressures of 40 to 50 mmHg. Laborlike fetal head compression with an intensity of 50 to 70 mmHg and a duration of one minute resulted in a 30 to 60% fall in PtCO2. Fetal PaO2 remained stable in all experiments. The present findings indicate that values of PtCO2 during fetal head compression do not reflect fetal arterial oxygen tension. This questions the reliability of transcutaneous PO2 monitoring as a method of intrapartum surveillance.     

Fetal head molding. Diagnosis by ultrasound and a review of the literature

Head molding refers to changes in cranial bone relationships that occur in response to external compression force. In the normal term labor with vertex presentation, the suboccipito-bregmatic diameter shortens and the mentovertical diameter lengthens. This is accomplished partially through the unbending or straightening of the parietal bones rather than the frequently taught mechanism of overlapping sutures. The occipital and frontal bones may also contribute by an inward movement of their apex, using their basal portions as a hinge. A locking mechanism may occur in protracted labors as the free edges of the cranial bones are forced into one another, preventing further molding and providing more protection for the fetal brain. The preterm skull has weaker material properties and wider sutures. Thus, more molding at lower pressures is possible and the protective effect of "locking" may not be operational. A case of extreme antenatal preterm fetal head molding discovered at ultrasound is presented as an introduction to review the literature regarding molding.     

Transabdominal ultrasound assessment of the fetal head and the accuracy of vacuum cup application.

OBJECTIVE: To investigate whether the accuracy of vacuum cup placement can be improved by intrapartum ultrasound assessment of the fetal head position during the second stage of labor prior to vacuum extraction for prolonged second stage. METHODS: 50 women undergoing vacuum extraction for prolonged second stage were randomly allocated to either digital examination (n=25) or digital examination together with transabdominal intrapartum ultrasound (n=25) prior to vacuum extraction by the attending obstetrician. The distance between the centre of the chignon and the flexion point was then measured by a midwife immediately after delivery. The flexion point was defined as 6 cm posterior to the anterior fontanelle or 3 cm anterior to the posterior fontanelle. RESULTS: There were no statistically significant differences in the demographic data, duration of labor, incidence of induction/augmentation, and intrapartum complications between the two groups. The mean distance between the centre of the chignon and the flexion point was 2.1+/-1.3 cm in the group with digital examination and ultrasound assessment and 2.8+/-1.0 cm in the group with digital examination alone. The difference in the mean distance between the two groups was statistically significant (p=0.039). CONCLUSION: Intrapartum transabdominal ultrasound assessment of the fetal head position during the second stage of labor improves the accuracy of vacuum cup placement during vacuum extraction for prolonged second stage.     

Use of femur length measured by ultrasonography to predict fetal maturity

The ultrasonographic criteria of biparietal diameter greater than or equal to 9.2 cm and a grade III placenta have been shown to correlate with fetal maturity in the fetus of a nondiabetic mother in our population. These two criteria have helped reduce the incidence of third-trimester amniocenteses by 66.6% at our institution. Occasionally, however, because of fetal position, we are unable to obtain an accurate biparietal diameter. We therefore carried out a prospective study of 120 patients to evaluate the relationship between femur length of greater than or equal to 7.3 cm and fetal maturity. In this study, the addition of the femur length criterion increased the specificity of the ultrasonographic criteria for fetal maturity from 66.6% to 85%. The data suggest that femur length could be used along with the biparietal diameter and placental grade as an alternative to amniocentesis in term nondiabetic pregnancies.     

The measurement of fetal growth during pregnancy by ultra-sound (B-scan).

We have followed fetal growth by ultrasonographic B-scans. In addition to percentile curves of the biparietal skull diameter we have established percentile curves for measurements of the fetal trunk (sagittal thoracic diameter and length of trunk). The percentile curves for the biparietal diameter were obtained from 5400 individual measurements; the percentile curves for the trunk measurements utilized 1300 individual measurements. These cases were from almost entirely unselected material from our special prenatal clinic. This resulted in a larger variation than the percentile curves for biparietal diameter of other authors [Campbell and Newman]. However, these authors selected their material for "normal pregnancy" while we insured that neither "corrections" of the normal variation nor subjective criteria for exclusion have introduced a systematic error. The advantages of ultrasonography for monitoring of the pregnancy are self-evident: repeated examinations are possible, the examination takes little time, and the method is safe. The determination of the biparietal diameter for estimation of fetal development alone is insufficient because trunk measurements may indicate developmental disturbances (dystrophy and hypertrophy) before the growth of the biparietal diameter of the skull is affected. Furthermore, comparison of the fetal skull and trunk measurement may indicate errors in measurement or malformations (hydrocephalus, microcephalus). The following percentile curves are illustrated graphically: 1. Gestational age versus biparietal diameter (Fig. 1). 2. Biparietal diameter versus weeks of gestation (Fig. 2). 3. Length of gestation versus sagittal thoracic diameter (Fig. 3). 4. Length of gestation versus length of trunk (Fig. 4). 5. Sagittal thoracic diameter versus length of trunk (Fig. 5).     

Cerebellar measurements with ultrasonography in the evaluation of fetal growth and development

A prospective study of ultrasonography was conducted in 371 normal pregnant women, with gestational ages ranging from 13 weeks to 40 weeks. Several biometric measurements were obtained including the transverse cerebellar diameter, the biparietal diameter, the occipitofrontal diameter, and the calculated head circumference. Curvilinear relationships were found between the transverse diameter of the cerebellum (measured in millimeters), and the gestational age (R2 = 0.948; P = 0.001), the biparietal diameter (R2 = 0.956; P = 0.0001), and the head circumference (R2 = 0.969; P = 0.0001). A nomogram of cerebellar measurements estimating gestational age and predicting the biparietal diameter and head circumference was generated. Throughout pregnancy the establishment of normative cerebellar measurements allows for the estimation of gestational age that is independent of the shape of the fetal head and offers potential for evaluation of abnormal fetal growth and anomalous development of the central nervous system.     

Ultrasonographic dating of pregnancy causes significant errors in Down syndrome risk assessment that may be minimized by use of biparietal diameter-based means.

OBJECTIVES: Gestational dates assessed by ultrasonographic measurement of fetal dimensions are usually quoted in terms of complete weeks because the uncertainty of ultrasonographic measurement is approximately +/- 7 days. This study examines the effect of ultrasonographic dating on Down syndrome risk assessment. STUDY DESIGN: The effect of small changes in measured biparietal diameter resulting in a change in estimated gestational week and the benefits of a more precise measure of fetal gestational age (raw biparietal diameter) are examined mathematically. RESULTS: If maternal serum alpha-fetoprotein and human chorionic gonadotropin are used to assess Down syndrome risk, risks assessed with ultrasonographically determined dates may be less than or equal to 45% too high for fetuses with biparietal diameter at the lowest end of the size band and less than or equal to 22% too low with biparietal diameter at the top of the size band. If the results for maternal serum alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol are used, these figures become less than or equal to 150% and less than or equal to 60%, respectively. CONCLUSION: If ultrasonography is used to assess gestational age, the raw biparietal diameter and not the estimated week of gestation must be used to derive means for calculation of multiples of the mean.     

Increment of the fetal biparietal diameter during normal pregnancy,as determined by ultrasound

The fetal biparietal diameter was measured by ultrasound during normal pregnancy. 1076 measurements were performed. For each week of pregnancy, from 23 until 43 weeks, the mean, percentiles and smoothed percentiles were determined. From statistical analysis no influence of fetal sex and maternal parity on the fetal biparietal diameter was found. From the 50th percentile the weekly increment of the fetal biparietal diameter was calculated.     

Diminished growth in fetuses born preterm after spontaneous labor or rupture of membranes

We examined biparietal diameter, abdominal circumference, and birth weight in 148 preterm infants to assess fetal growth. A statistically significant proportion of preterm fetuses had biparietal diameter and abdominal circumference values below the fiftieth and tenth percentile levels as compared with that expected in normal fetuses. Similarly, birth weight of infants in the study fell significantly below the fiftieth and tenth percentiles relative to Brenner's curve. We conclude that diminished fetal growth is associated with early delivery secondary to preterm labor or preterm premature rupture of membranes or both. Additionally, since biparietal diameters in preterm fetuses are smaller than those of normal fetuses the prediction of gestational age by cephalometry should be advanced by 7 to 10 days.     

Levels of agreement between clinical examination and transabdominal ultrasound evaluation of fetal head position in the second stage of labor

Aim: To compare transvaginal digital examination performed by residents and attending physicians to transabdominal suprapubic ultrasound in the evaluation of fetal head position in the second stage of labor.

Methods: A prospective study was conducted at a tertiary center and included pregnant women at term, with normal singleton cephalic presentation fetuses. All patients had ruptured membranes and were evaluated during the second stage of labor. Fetal head position was assessed consecutively by two clinicians (one resident and one attending physician). Afterwards, transabdominal suprapubic ultrasound was performed by another observer. Examiners were blinded to each other’s findings. Cohen’s kappa test was used to assess the degree of agreement between the evaluation methods.

Results: One-hundred sixty-one women were included. Transvaginal examination was consistent with the ultrasound in 45.0% of cases (95% CI: 37–53%) when the examination was performed by residents (k?=?0.349) and in 67% (95% CI: 60–74%) if the attending physician carried out the evaluation (k?=?0.604). When considering only the anterior positions, the Cohen’s kappa test was 0.426 and 0.709, respectively.

Conclusion: Transabdominal suprapubic ultrasound improved the accuracy of the evaluation of fetal head position, namely when transvaginal digital examination was performed by residents. This may be important especially when instrumental deliveries are considered.     

Second-stage fetal tachycardia and neonatal infection

Forty fetuses who had mild or marked tachycardia during the final 10 minutes of the second stage of labor were evaluated for neonatal infection. Prolonged sepsis/pneumonia occurred in 10 of the 40 infants (25%), three of eight (38%) with marked tachycardia, seven of 32 (22%) with mild tachycardia, and in only one of 167 control infants who had a normal second-stage fetal heart rate (0.6%). None of the 40 women with fetal tachycardia or the 167 control subjects had any intrapartum fever or other evidence of acute chorioamnionitis. Persistent fetal tachycardia during the second stage of labor defines a population at increased risk for subsequent neonatal sepsis/pneumonia. This population will require prolonged, expert neonatal care.     

Ultrasound measurement of fetal abdominal circumference and the ratio of biparietal diameter to transverse abdominal diameter in a mixed Nigerian population

The fetal abdominal circumference (FAC) and biparietal diameter to transverse abdominal diameter ratio (BPD/TAD) were measured by ultrasound in 219 normal pregnant Nigerian women from 20 weeks until term using the cross-sectional method. There was a progressive linear growth of the FAC and a consistent standard deviation throughout the study period. When compared to caucasian growth curves, the curve shapes were identical but the FAC values were consistently less for each week of gestation in our Nigerian sample. The BPD/TAD ratio showed a progressive fall from 20 weeks until term similar to that previously noted for fetal head circumference to abdominal circumference ratio, indicating that this parameter may also be useful for predicting abnormal fetal growth.     

第二产程胎心监护异常的处理及临床意义

目的 探讨第二产程胎心监护异常者的分娩方式,及其与产妇并发症和围产儿结局的关系。方法 回顾性分析我院足月单胎头位分娩产妇第二产程中胎心率（FHR）正常的111例（对照组）和胎心率异常的121例（观察组）的资料。结果 FHR异常的发生率为52.2%（121／232）,异常胎心率类型包知中、重度变异减速（VD）81例,占66.9%;晚期减速（LD）27例,占22.3%,其中仅1例发生连续LD;延长减速（PD）4例,占3.3%;VD合并LD2例,占1.7%;VD合并PD3例,占2.5%;基线变异减弱4例,占3.3%。对照组中,阴道助产13例（11.7%）,顺产98例（88.3%）;观察组中,顺产86例（71.1%）,阴道助产35例（28.9%）,其中29例（82.9%）为FHR异常而施术者,两组间比较,差异有显著性（P＜0.05）。观察组、对照组新生儿窒息的发生率（分别为5.0%、1.8%）及产伤的发生率（14.3%、15.4%）比较,差异均无显著性（P＞0.05）;观察组中有1例产妇会阴Ⅲ度撕伤。结论 第二产程中FHR异常的发生率高,多为产程中胎头受压或脐带受压而引起的迷走神经反射或暂时性子宫胎盘血流减少,并非缺氧所致,不必急于干预,以免造成母、儿损伤。     

Fetal liver measurements by ultrasonography

A total of 378 measurements of fetal liver size were made from 18 weeks gestation through term. Statistical analysis of the results showed a highly significant correlation between fetal liver measurements and gestational age, biparietal diameter, and fetal femur length (R = 0.93, R = 0.89, R = 0.89, respectively). Ultrasonic measurement of the fetal liver is a reliable indicator of fetal growth in the third trimester, as growth rates of the biparietal diameter and head circumference are blunt. Furthermore, consecutive measurements of fetal liver size enhance the detection of symmetrical, fetal growth, by acquisition of various ultrasonic parameters such as biparietal diameter, fetal femur length, fetal abdominal circumference and so forth.     

Increased beat-to-beat variability during uterine contractions: A common association in uncomplicated labor

A computerized system was used during labor to provide a quantitative and objective analysis of fetal heart rate, beat-to-beat variability, and uterine contractions. Twenty-nine healthy pregnant women at term participated in this study. Each woman was studied for a 40-minute period during the active phase of spontaneous labor. The results indicate that beat-to-beat variability rises from a value of 4.62 ± 1.11 (mean ± SD) between contractions to 6.86 ± 1.53 during contractions. This rise is significant (p < 0.01). At the same time, changes in fetal heart rate are small, inconsistent, and not significant. We conclude that an increased beat-to-beat variability is commonly associated with uterine contractions in normal fetuses. This increase is probably due to mild hypoxia caused by decreased perfusion of the placenta and to increased vagal tone caused by fetal head compression.