Prediction of birth weight by ultrasound in the third trimester

OBJECTIVE: To compare the accuracy of predicted birth weight by the gestation-adjusted projection method using ultrasonographic measurements obtained just before and at term. METHODS: The study group comprised patients with singleton pregnancies who underwent sonograms between 34.0 and 36.9 weeks' gestation (period 1) and at 37 weeks and beyond (period 2). The mean error in birth weight prediction, absolute birth weight error, and signed and absolute percent errors were compared with paired t tests. Thus, each patient served as her own control. RESULTS: The study included 138 patients undergoing 276 sonograms. The mean absolute error of the predicted birth weight was smaller for period 1 than for period 2 (197 +/- 167 g compared with 235 +/- 209 g, P =.019). The mean absolute percent error was 6.2 +/- 5.2% for period 1 compared with 7.4 +/- 6.3% for period 2 (P =.019). These same trends were observed when fetuses with suspected growth abnormalities were examined separately. Averaging data from both gestational periods did not improve the prediction of birth weight. CONCLUSION: Sonograms between 34.0 and 36. 9 weeks' gestation allow for more accurate prediction of birth weight than sonograms later in gestation. Though these differences are small and not clinically significant, this study indicates that serial sonograms in the late third trimester do not improve the ability to predict birth weight, even in abnormally grown fetuses. A single sonogram between 34 and 37 weeks' gestation is recommended for prediction of birth weight.     

Twin weight discordance and maternal weight gain in twin pregnancies.

OBJECTIVE: To evaluate the association between twin weight discordance and maternal weight change during the gestational period. METHOD: One hundred forty-seven twin pregnancies (Group A: <25%, Group B: > or =25% birth weight discordance) were analyzed using Student's t-test, chi(2)-test, and two-way ANOVA at three gestational intervals: before 18 weeks, 18 to 28 weeks, and 28 weeks to birth. RESULT: There was no statistically significant difference between the two groups involving maternal age, parity, duration of pregnancy, height, pregravid weight, and conception method. Group A showed a pattern of constantly increasing maternal weight without a significant change in the twin weight discordance throughout gestation. However, Group B showed a fluctuation in maternal BMI with remarkably elevated twin weight discordance at 28 weeks to birth. CONCLUSION: The results suggest that in twin pregnancies constant maternal weight gain throughout gestation is important for maintaining a twin weight discordance of less than 25%.     

Sonographic prediction of twin birth weight discordance

OBJECTIVE: To assess the accuracy of sonographic prediction of clinically significant twin birth weight discordance (25% or greater) and to determine whether this accuracy is affected by defined fetal and maternal variables. METHODS: Using an established database, we reviewed 338 twin gestations delivered over 10 years as a retrospective cohort. Estimation of fetal weight was calculated by applying the Hadlock formula using composite fetal biometry. Intertwin weight discordance was calculated as the difference in the estimated or actual twin weights (A-B) divided by the weight of the larger twin and was expressed as a percentage. Statistical evaluation included validity (sensitivity, specificity, and predictive values) and reliability assessment of ultrasonographic measurements (intraclass correlation coefficients). Multivariable analysis was performed. RESULTS: Of 338 twin gestations, 192 (57%) twin pairs met inclusion criteria. Sonographic prediction of actual intertwin birth weight discordance of 25% or greater had a sensitivity of 55%, specificity of 97%, positive predictive value of 82%, and negative predictive value of 91%. The reliability of estimating intertwin birth weight discordance by ultrasonography was moderately high (intraclass correlation coefficient =.700; 95% confidence interval [CI].620,.765). Multivariable analysis revealed no significant effects of individual maternal or fetal factors on the accuracy of ultrasonographic prediction of intertwin birth weight discordance. CONCLUSION: Sonographic prediction of actual intertwin birth weight discordance of 25% or greater within 16 days of delivery appears to be a valid and reliable method for clinical use. Predictive accuracy is independent of other identifiable maternal or fetal variables.     

The relation between inter-twin birth weight discordance and total twin birth weight

Objective: We tested the hypothesis that the frequency of growth discordance among twins is not related to the uterine capacity for carrying twins.Method: We counted and compared the frequencies of birth weight discordance of more than 25% in an unlike-sexed twin cohort (n = 1244) and in a population-based twin cohort (n = 7570) across the deciles of the total twin birth weight (twin A + twin B) distribution. The birth order of the heavier twin was noted.Results: Similar frequencies of discordant pairs were found in both cohorts (11% and 12%, respectively; Mantel-Haenszel χ² test: P = .131, odds ratio (OR) 0.9, 99% confidence interval (CI) 0.67, 1.11; Woolf test for heterogeneity: two-tailed P = .472). In the discordant pairs, twin A was considerably more often the heavier twin in all birth weight deciles (unlike-sexed cohort: P < 10⁻⁸, OR 5.9, 99% CI 3.0, 11.7; population-based cohort: P < 10⁻⁸, OR 3.1, 99% CI 2.3, 4.0), and in both cohorts (inter-cohort difference: P = .109, OR 1.4, 99% CI 0.83, 2.32). Both cohorts showed a similar nonlinear trend: given that X = decile order, discordance decreased as a function of 22.0 − 6.54 ln[X] for the unlike-sexed twins cohort and 23.0 − 8.18 ln[X] for the population-based cohort, with r values of 0.967.Conclusion: The more favorable the uterine milieu for carrying twins, the smaller the likelihood of discordant twin growth. Birth order of the heavier twin appears to be an integral part of the discordance phenomenon. The similarity of the cohorts suggests that these conclusions are valid for both like and unlike-sexed twins.     

Gestational age-specific distribution of twin birth weight discordance

AIM: To examine the gestational age-specific distribution of twin birth weight discordance. METHODS: We analyzed all liveborn twin sets between 28 and 40 weeks' gestation from the United States 1995-1998 Multiple Matched Birth Data Set compiled by the National Center for Health Statistics. We calculated the 50th and 95th percentiles of birth weight discordance at each gestational age. Neonatal mortality rates were calculated for discordant twins at the 95th percentile of birth weight discordance for each gestational age. RESULTS: At older gestational ages, the 95th percentile of birth weight discordance resulted in an inter-twin birth weight difference of approximately 25%, a value often used to define twins as birth weight discordant. However, at earlier gestational ages, the 95th percentile of birth weight discordance was greater, reaching nearly 50% at 28 weeks. CONCLUSIONS: The inter-twin birth weight difference at the 95th percentile is greater at lower gestational ages, possibly illustrating the different nature or severity of twin birth weight discordance at an earlier gestational age.     

Prediction of light-for-gestational age at delivery in twin pregnancies: an evaluation of fetal weight deviation and growth discordance measured by ultrasound.

The purpose of this retrospective study was to evaluate and discuss different ultrasound methods widely used, among other things, as predictors for light-for-gestational age (LGA) in twin pregnancies. The methods evaluated and compared as predictors for LGA at birth were: (1) Difference between twins in biparietal diameter; (2) difference in abdominal diameter; (3) the percentage difference in estimated fetal weight between twins; and (4) estimation of the weight deviation from the expected weight during pregnancy. The study comprised 66 twin pregnancies, examined by ultrasound scanning less than 15 days before delivery. Using Relative Operating Characteristic curves (ROC curves) estimated fetal weight deviation was the most sensitive and specific of the methods. It is stressed that fetal discordance is not the appropriate predictor of LGA at birth in twin pregnancies.     

Detection by ultrasound of abnormality in twin pregnancies during the second trimester

Five cases of abnormality in twin pregnancies, detected by ultrasound examination during the second trimester, are reported. In four pregnancies there was a fetal malformation: discordant anencephaly, a monozygotic, heterokaryotypic twin pregnancy with coexistant Turner's syndrome and intrauterine death, concordant body stalk syndrome, and a dicephalus monster. In the other pregnancy one fetus dies in utero to become a fetus papyraceous. Four of the pregnancies were associated with raised levels of maternal serum alpha-fetoprotein, by singleton standards. Ultrasound examination proved of value in each case. Three pregnancies were terminated.     

Detection by ultrasound of abnormality in twin pregnancies during the second trimester

Summary. Five cases of abnormality in twin pregnancies, detected by ultrasound examination during the second trimester, are reported. In four pregnancies there was a fetal malformation: discordant anencephaly, a monozygotic, heterokaryotypic twin pregnancy with coexistant Turner's syndrome and intrauterine death, concordant body stalk syndrome, and a dicephalus monster. In the other pregnancy one fetus dies in utero to become a fetus papyraceous. Four of the pregnancies were associated with raised levels of maternal serum α-fetoprotein, by singleton standards. Ultrasound examination proved of value in each case. Three pregnancies were terminated.     

The effect of birth weight discordance on twin neonatal mortality

OBJECTIVE: To estimate the association between birth weight discordance and neonatal mortality controlling for the effects of fetal growth, and to understand the differences in the incidence of mortality between larger and smaller infants. METHODS: This analysis is based on the National Center for Health Statistics matched multiple birth data set file containing all twin births in the United States from 1995 through 1997. Birth weight discordance was grouped into four levels (15-19%, 20-24%, 25-29%, and 30% or more). Generalized estimating equations were used to obtain adjusted odds ratios and 95% confidence intervals to estimate the mortality risk associated with discordance after adjusting for fetal growth. RESULTS: Mortality was 11 times higher among highly discordant smaller twins (30% or more) compared with nondiscordant smaller twins (43.4 and 3.8 per 1000, respectively). Risk estimates ranged from 1.08 (95% confidence interval 0.85, 1.38) among 15-19% discordant twins to 2.05 (95% confidence interval 1.66, 2.51) among 30% or more discordant twins. Larger twins had similar risk estimates. After accounting for the association between fetal growth and discordance, mortality risk was substantially higher among smaller and larger twins who were highly discordant (30% or more). In addition, there was little difference in the magnitude of risk estimates between highly discordant smaller and larger twins. CONCLUSION: After controlling for fetal growth, smaller and larger twins affected by higher levels of birth weight discordance (25% or more) remain at disproportionate risk for neonatal mortality when compared with other smaller or larger twins. Additionally, smaller twins do not have an elevated risk compared with larger twins after adjusting for their different fetal growth distributions.     

Maternal serum alpha-fetoprotein and birth weight in twin pregnancies.

In 102 twin pregnancies the mean birth weight of each pair showed a statistically significant negative association with maternal serum alpha-fetoprotein (AFP) levels early in pregnancy. Women with AFP levels of four or more times the median value for singleton pregnancies gave birth to infants with a median birth weight 660 g less than that of infants born to women with AFP levels between 1.0 and 1.5 times the median for singleton pregnancies. Maternal serum AFP has been shown to be an early predictor of low birth weight delivery in singleton pregnancies. Our results indicate that this is also true in twin pregnancies.     

Prediction of intra-twin birth weight discordance by binary logistic regression analysis

AIMS: Identification of women at high risk of intra-twin birth weight discordance is helpful in obstetric care of these pregnancies. The aim of this study is to establish an intra-twin birth weight discordance prediction model. METHODS: We created an intra-twin birth weight discordance prediction model by logistic regression, based on the 1995-1997 register twin birth data of the USA. The twin sets were randomly divided into two groups: group 1 to establish the prediction model and group 2 to validate the prediction model. Intra-twin birth weight discordance was defined as birth weight discordance > 25%. The prediction model was validated by receiver operating characteristic curve. RESULTS: A birth weight discordance prediction model including maternal age (beta = 0.069), parity (beta = 0.250), fetal gender concordance (beta = 0.041), maternal hypertension (beta = 0.368), eclampsia (beta = 0.316), other medical complication (beta = 0.165), and smoking (beta = 0.164) was established, yielded a 0.558 area under the receiver operating characteristic curve. The sensitivity, specificity, and positive predictive values were 38.1, 69.7, and 10.8%, respectively, at the cut-off value of 0.09 in group 2. CONCLUSION: A birth weight discordance prediction model that includes seven variables available during pregnancy has been established with acceptable diagnostic performance.     

The effects of birth weight discordance and prematurity on twin neonatal outcome

OBJECTIVE: The purpose of this study was to determine the effect of birth weight discordance (BWD) and prematurity on twin neonatal outcome by measuring Apgar scores and blood glucose concentrations at birth. METHODS: This was a retrospective cross-sectional study. All twins born at NY Methodist Hospital between January 1998 and December 2001 were eligible. Excluded were fetal deaths, maternal systemic disease, maternal infections, major neonatal malformations, neonates with birth weight < 500 g and multiple gestation greater than 2. BWD was defined as intrapair difference in birth weight expressed as percentage of the larger twin greater than 20% and prematurity as gestation of less than 37 weeks. Hypoglycemia was defined as blood glucose concentration < 40 mg/dl. RESULTS: There were 75 (48%) preterm and 80 (52%) term twin pairs. Nineteen (12%) of the preterm and 15 (9.6%) of the term showed BWD. Mean Apgar scores at 1 and 5 minutes were higher for the term twins as expected. Neither prematurity nor hypoglycemia was present predominantly in BWD twins. Twelve of the preterm and six of the term BWD twins showed evidence of hypoglycemia. CONCLUSION: Hypoglycemia in the early hours of postnatal life is relatively common in preterm BWD twins. Blood glucose measurement using reagent strips is an efficient way of monitoring blood glucose concentrations in these infants.     

Outcome of twin pregnancies according to intrapair birth weight differences

OBJECTIVE: To assess the clinical significance of twin intrapair birth weight differences. METHODS: This was a retrospective study of twin pregnancy outcomes. Intrapair birth weight differences were stratified into the following six groups: 14% or less, 15-20%, 21-25%, 26-30%, 31-40%, and 41% or more using the larger infant as the growth standard. Statistical analysis was done using the Mantel-Haenzel chi2 test. RESULTS: We studied 1370 consecutive women who delivered at Parkland Hospital, Dallas, Texas, between January 1, 1988, and December 31, 1996, and had twin gestations and live births or fetal deaths within 7 days of delivery. Greater birth weight discordance was significantly associated with preterm delivery due to intervention (P<.001). Noncephalic-cephalic presentations and cesarean delivery were also associated with greater discordance (P = .001 and .02, respectively). Neonatal morbidities, including low birth weight, intensive care admission, and respiratory distress, were all associated with higher birth weight discordance. Fetal abnormalities were more common with increased discordance (P<.001). Greater birth weight discordance was also associated with intrauterine fetal death. There were no differences in outcome for the smaller compared with the larger twin of the twin pair. CONCLUSION: Twin birth weight discordance is problematic because severe divergent fetal growth increases the risk of fetal death and leads to obstetric intervention and consequent neonatal morbidity due to prematurity.     

Adaptive growth restriction as a pattern of birth weight discordance in twin gestations

OBJECTIVE: To challenge the hypothesis that discordant growth is a normal variation by relating birth weight discordance to total twin birth weight. METHODS Among 12,565 Israeli live-born twin pairs (1993-98), we compared total twin birth weight decile, the frequencies of three levels of discordance in the general population, over 25% discordance between like- versus unlike-sex pairs, and over 25% discordance between pairs delivered by primiparas versus multiparas. RESULTS: We found a marked change in the best-fit correlation function with increased discordance: level 15-24.9% was inversely linear whereas levels 25-34.9% and over 34.9% were inversely logarithmic (R(2) =.47,.88, and.9, respectively). The best-fit correlation of frequencies of more than 25% discordance was inversely logarithmic and similar in like- and unlike-sexed twins across deciles functions (P =.7, odds ratio [OR] 1.0, 95% confidence interval [CI] 0.9, 1.2). The overall frequencies of discordance were also similar (9.3% versus 10.2%, P =.11, OR 0.9, 95% CI 0.8, 1.0). The frequencies of primiparas decreased linearly (R(2) =.98) and the frequencies of more than 25% discordant pairs in multiparas and primiparas across the deciles had similar inversely logarithmic patterns (P =.55, OR 1.0, 95% CI 0.9, 1.2). Discordance over 25% was significantly more frequent among primiparas (P <.001, OR 1.45, 95% CI 1.3, 1.6). CONCLUSION: The observed patterns of birth weight discordance did not substantiate normal variation but an adaptive growth restriction that might explain why the likelihood of discordant growth decreases as total twin birth weight increases.     

The intrauterine ponderal index in relation to birth weight discordance in twin gestations

Objective: To establish the relationship between the fetal ponderal index and birth weight discordance in twins. Method: The fetal ponderal index (estimated fetal weight ÷ femur length³) was calculated in 86 pairs of twins delivered within 2 weeks of the last sonography and analyzed in relation to birth weight discordance. Results: A weak but significant correlation between fetal ponderal index and birth weight (r = 0.26, P < 0.0007) but no correlation with gestational age (r = 0.035, P = 0.65) were found. Members of concordant pairs (<15% birth weight difference) had a significantly higher fetal ponderal index compared with members of mildly (15–25%) discordant pairs (P < 0.02), but not as compared with members of severely discordant (>25%) pairs. Conclusion: The characteristics of the fetal ponderal index in twins are similar to those in singletons. Fetal size seems to be diminished in severe but not in mild discordants. However, in its present form, the fetal ponderal index is a poor predictor of discordant growth and therefore should be employed cautiously in twin gestations.     

First trimester prediction of growth discordance in twin gestations

OBJECTIVE: The purpose of this study was to determine whether first trimester ultrasound scanning can identify twin gestations that are at risk for subsequent growth discordance. STUDY DESIGN: Ultrasound examinations of dichorionic twin pregnancies between 11 and 14 weeks of gestation were evaluated for growth discordance with crown-rump length. Pregnancies that were complicated by fetal death or anomalies were excluded from the analysis. Birth weight discordance was defined as >or=20% difference in birth weight, relative to the larger twin. Fisher's exact, Mann Whitney U, and Spearman rho tests were used for statistical analysis. RESULTS: Of 130 twin pregnancies, 16 pregnancies (12.3%) had discordant birth weight. Crown-rump length disparity was correlated positively with birth weight discordance (r=0.31; P<.001). Of pregnancies with a discrepancy of 3 days discrepancy (P=.004), which resulted in a likelihood ratio of 5.9 for having discordant birth weight. CONCLUSION: Twins who are ultimately discordant at birth may exhibit differences in growth as early as 11 to 14 weeks of gestation.     

The association between maternal weight gain and spontaneous preterm birth in twin pregnancies

Abstract

Objective: To estimate the association between maternal weight gain and SPTB in twin pregnancies.

Methods: A case-control study of patients with twin pregnancies and a normal prepregnancy BMI (18.5–24.9?kg/m²) in one maternal-fetal medicine practice from 2005 to 2013. We reviewed maternal weight in six time periods: prepregnancy, 12–15 6/7 weeks, 16–19 6/7 weeks, 20–23 6/7 weeks, 24–27 6/7 weeks and 28–31 6/7 weeks. We compared maternal weight gain patterns across pregnancy between patients who did and did not have SPTB <32 weeks. Student’s t-test and chi-square were used for analysis.

Results: In total, 382 patients were included, 29 (7.6%) of whom had SPTB <32 weeks. The baseline height, weight and BMI did not differ between the groups, nor did maternal age, IVF status, race or chorionicity. Patients with SPTB <32 weeks had significantly less weight gain as early as 15 6/7 weeks (2.9?±?4.6 versus 7.3?±?6.6?lb, p?<?0.001), and this continued until 31 6/7 weeks (25.3?±?8.7 versus 30.8?±?10.9?lb, p?=?0.037).

Conclusions: In twin pregnancies with a normal prepregnancy BMI, there is a significant association between SPTB <32 weeks and lower maternal weight gain, particularly prior to 16 weeks. Future studies are needed to test if prepregnancy or early nutritional interventions in twin pregnancies can reduce the risk of preterm birth and improve neonatal outcomes in this high-risk population.     

The relation between maternal plasma alpha-fetoprotein and birth weight in twin pregnancies.

In the course of routine screening for neural tube defects, maternal plasma alpha-fetoprotein (AFP) was measured between 15 and 23 weeks of gestation in 64 twin pregnancies. Women with AFP levels more than twice the median for singleton pregnancies gave birth to infants with significantly decreased birth weights. Women with AFP less than the median also tended to produce twins with decreased birth weights. The distribution of gestations at delivery suggested that in twin pregnancies low AFP values gave an early warning of growth retardation while high values signal possible premature delivery.