Standards of Birth Weight in Twin Gestations Stratified by Placental Chorionicity

Objective: To establish fetal growth nomograms for twin gestations, categorized by placental chorionicity, and to compare them with those of published singleton and twin nomograms.Methods: Computerized data files of live births of all twins delivered between January 1990 and October 1996 at Saint Peter’s Medical Center were used. Birth weight curves corresponding to the fifth, tenth, 50th, 90th, and 95th percentiles were derived separately for twins with monochorionic and dichorionic placentation. We generated the curves by applying the method of generalized estimating equations, after adjusting for the potential intracluster correlation due to twinning. The curves were then smoothed on the basis of nonparametric restricted cubic splines to derive (smoothed) birth weight percentiles. We then compared our twin birth weight nomogram to six previously published singleton and two twin nomograms published previously for predicting small for gestational age infants (defined as birth weight below the tenth percentile).Results: Among 1302 twin fetuses, 272 (21%) were monochorionic. Twins from monochorionic gestations weighed, on average, 66.1 g (standard deviation 28.4 g, P = .02) less than twins from dichorionic gestations after correcting for gestational age. Twin curves based on parity (nulliparity versus multiparity) were not different from each other. Analyses indicate that all previously published singleton nomograms approximate twin growth reasonably well between 32 and 34 weeks, but they underestimate twin growth at earlier gestational ages (between 25 and 32 weeks) and overestimate twin growth beyond 34 weeks’ gestation. Similarly, a comparison of previously published twin nomograms with those of ours indicates that the growth standards in our population were similar to those in other published twin nomograms.Conclusion: We recommend that future epidemiologic and clinical studies use twin nomograms to identify growth-restricted twin fetuses. Moreover, because fetal growth is influenced by placental chorionicity, we recommend that fetal growth assessment in twin gestations consider placental chorionicity, whenever the information is available.     

Birth weight by gestational age in twin pregnancies: analysis of 661 pairs.

The mortality of twin infants is four to five times higher than that of singletons, and one-half to two-thirds of all twins weigh < 2,500 g at birth. The appropriate interpretation of fetal growth throughout pregnancy is dependent upon the availability of adequate standards. We reviewed 661 pairs of live twin infants born at Chang Gung Memorial Hospital from 1979 to 1990. The frequency of twin births was 1.17% (1:86), and the ratio of males to females was 1.03. The frequency of preterm births (< 37 weeks) was 36.9%, the frequency of low birth weight (< 2,500 g) was 47.9% and very low birth weight (< 1,500 g) was 6.7%. A fetus grows most rapidly from the 32nd to the 35th week of gestation (200 g per week). The growth was 145 g per week from the 28th to the 32nd week and from the 35th to the 38th week of gestation. After the 38th week, the mean birth weight increased by only 35 g per week. Compared with a singleton birth, the mean birth weight of twins was about 100 g lighter during the 28th to the 32nd week, then the difference increased gradually to about 500 g at term.     

Intrauterine growth of live-born twins in the area of Sibenik, Split and Zadar

By a retrospective analysis the authors studied live-born twins by gestation weeks and birth weight and height: there were 1,195 first-born and 1,189 second-born twins, all from three neighbouring Dalmatian towns (Split, Sibenik and Zadar). A common curve was worked out of the intrauterine growth of both the first and the second twins and a separate curve of each of them. The curves have shown that the twins' birth weight was increassing up to the 40th week of pregnancy; in the 41st week the curve already went down. The authors conclude that twin pregnancy should not last more than 40 weeks.     

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.     

Fetal serum levels of insulin, growth hormone and insulin-like growth factor-I in concordant and discordant twin gestations

OBJECTIVE: To examine the role of insulin, growth hormone and insulin-like growth factor (IGF)-I in concordant and discordant twin pairs. METHODS: Umbilical cord serum samples were obtained from 20 twin pairs with weight discordancy (intertwin birth weight difference > 20%) and from 20 concordant twins (intertwin birth weight difference < 20%), both groups of similar gestational age, gravidity, and parity. The serum samples were analyzed for the levels of IGF-I, growth hormone and insulin in both maternal and fetal compartments. RESULTS: Among the group of discordant twins, the normally grown twin, in all cases, had significantly higher cord serum IGF-I levels than their growth-restricted co-twin (108 +/- 73 ng/ml vs. 39 +/- 24 ng/ml; p < 0.01). There were no significant intertwin differences in the cord blood IGF-I levels in the concordant twin pairs (87 +/- 44 vs. 88 +/- 48 ng/ml; p = 0.986). Insulin and growth hormone levels did not correlate with intertwin birth weight differences. CONCLUSION: These data demonstrate that IGF-I is important in the regulation of both normal and restricted fetal growth in utero, and its action appears to be, at least in part, through an endocrine action. The precise role of growth hormone and insulin in fetal growth restriction remains uncertain.     

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.     

Fetal serum levels of insulin,growth hormone and insulin-like growth factor-I in concordant and discordant twin gestations

Objective: To examine the role of insulin, growth hormone and insulin-like growth factor (IGF)-I in concordant and discordant twin pairs. Methods: Umbilical cord serum samples were obtained from 20 twin pairs with weight discordancy (intertwin birth weight difference > 20%) and from 20 concordant twins (intertwin birth weight difference < 20%), both groups of similar gestational age, gravidity, and parity. The serum samples were analyzed for the levels of IGF-I, growth hormone and insulin in both maternal and fetal compartments. Results: Among the group of discordant twins, the normally grown twin, in all cases, had significantly higher cord serum IGF-I levels than their growth-restricted co-twin (108 &#45 73 ng/ml vs. 39 &#45 24 ng/ml; p < 0.01). There were no significant intertwin differences in the cord blood IGF-I levels in the concordant twin pairs (87 &#45 44 vs. 88 &#45 48 ng/ml; p = 0.986). Insulin and growth hormone levels did not correlate with intertwin birth weight differences. Conclusion: These data demonstrate that IGF-I is important in the regulation of both normal and restricted fetal growth in utero, and its action appears to be, at least in part, through an endocrine action. The precise role of growth hormone and insulin in fetal growth restriction remains uncertain.     

Contribution of Gestational Age and Birth Weight to Perinatal Viability in Singletons Versus Twins

The objective of this study was to determine the effects of birth weight and gestational age on twin vs. singleton mortality. Population-based analysis of live births, fetal deaths, and infant deaths by plurality in the United States from 1983 to 1986 was conducted. Seven mortality rates and relative risks (RRs) of twin vs. singleton mortality were calculated by birth weight, gestational age, and combined birth weight and gestational age. The mortality rates included fetal, perinatal, early neonatal, late neonatal, neonatal, postneonatal, and infant. Twins had 3–4 times the RRs of mortality compared to singletons, ranging from a RR of 2.71 for postneonatal mortality to a RR of 3.73 for late neonatal mortality. Generally, for birth weights of 2,800 g or less and gestational ages of 38 weeks or less, twins had lower combined birth weight and gestational age mortality rates and lower RRs. Between 1,900 and 2,799 g, mortality rates decreased then increased with advancing gestation between 31 and 42 weeks both more severely and consistently for twins than for singletons. In conclusion, twins have lower birth weight and gestational age-specific mortality rates and RRs than singletons below 2,800 g and 39 weeks. The “U”-shaped pattern of mortality beyond 38 weeks gestation, particularly for twins with birth weights below 2,500 g, reflects the combined influence of growth retardation and advancing gestation on mortality. The lowest mortalityfor twins is achieved at birth weights of 2,500-2,799gat35-38 weeks gestation. Only 1 in 7 twins is born within this “ideal window.” Efforts at reducing twin mortality should be directed toward reducing intrauterine growth retardation and achieving optimal timing for delivery.     

Intrauterine growth in twin pregnancies: prediction of fetal growth retardation

In 80 consecutive twin pregnancies, prenatal measurements of fetal biparietal diameter (BPD) and abdominal diameter were made and growth curves were calculated using routine ultrasound examinations. Nineteen percent of the infants were growth retarded. Growth retardation was found in both fetuses in four pregnancies and in one fetus in 22 other pregnancies. Linear regression analysis between birth weight and gestational age showed the standard deviation of birth weight to be proportional to gestational age. A more linear growth curve also was found when the mean fetal weight was calculated by use of the BPD and abdominal diameter measurements in the formula developed for singletons. The estimated weight compared with birth weight in 62 twins who had ultrasound examinations less than seven days before delivery showed a significant correlation (r = 0.89, P less than .001) with a coefficient of variation of 12.4%. The identification of intrauterine growth retardation (IUGR) in twin pregnancies by ultrasound had a sensitivity of 62%, a specificity of 98%, and a predictive value of positive and negative test of 93% and 83%, respectively.     

Fetal biometric parameters, twin type and birth weight difference. A longitudinal study

OBJECTIVE: To examine the relationship between twin type, divided by zygosity, chorionicity, and birth weight difference [more or less than 15% intertwin weight difference at delivery] on fetal biometric measurements, including biparietal diameter, transverse abdominal diameter, head and abdominal circumferences (AC) and head and abdominal areas, femur length (FL), transverse cerebellar diameter, cerebellar circumference and cerebellar area at 18, 23, 28 and 32 weeks of gestational age. STUDY DESIGN: A prospective and longitudinal study was done on 75 twin pairs that did not present the twin-twin transfusion syndrome (150 fetuses) divided into birth weight difference group I (<15%) and group II (>/=15%). The twin pairs were divided into three groups: dizygotic, monochorionic, and dichorionic-monozygotic. In each group the differences in various ultrasound indices were evaluated in reference to discordant growth or concordant growth. RESULTS: In our sample, there were no monozygotic twin pairs with dichorionic placentation with a birth weight difference of more than 15%. Significant associations of group and gestational age were found in dizygotic and monochorionic twins. Intrapair differences were significantly higher in group II (>/=15%) than in group I (<15%) for all fetal parameters studied except for AC, abdominal area and all cerebellar parameters. The value of these discrepancies increased according to gestational age except for FL. Significant interactions between group and zygosity type indicated that intrapair FL differences were more associated with group in monochorionic twins, whereas intrapair transverse cerebellar diameter differences were more associated with group in dizygotic twins. CONCLUSION: Our data show that most fetal biometric parameters are associated with birth weight discordancy. Abdominal area could be a relevant marker for twins with obstetric complications. Note that this is the first research that has studied a twin sample divided by both twin type and birth weight group.     

Birthweight percentiles by gestational age in multiple births. A population-based study of Norwegian twins and triplets

OBJECTIVE: To assess secular trends for birthweight by gestational age in twins in Norway and to develop current national birthweight standards by gestational age for twin and triplet births using population-based data. MATERIAL AND METHODS: The analysis of secular trends for birthweight and gestational age in twins was based on 32,379 twin livebirths (1967-95). Taking into account the observed secular trends in birthweight for 35-40 weeks of gestation, data on twins born during 1987-95 only were included in the calculation of birthweight percentiles for 35-40 weeks, while for lower and upper weeks, data on twins born during 1967-95 were used. The construction of birthweight-for-gestation curves for triplets was based on the data on 690 triplets. RESULTS: Whereas the overall mean birthweight and gestational age decreased in 1987-95 compared with the previous years, the mean birthweights by gestational age for the 35-40 weeks of gestation was significantly higher in 1987-95. Male twins weighed more than female twins throughout the gestation with consistent and significant differences from 27 to 42 weeks of gestation. Smoothed curves for birthweight-by-gestational-age percentiles of male and female twins are plotted. The birthweight-by-gestational-age curves of triplets were almost identical with twin curves before 30 weeks of gestation, starting to diverge from them progressively thereafter. The intrauterine growth of twin births also starts to differ markedly from singletons at approximately 30 weeks of gestation. CONCLUSION: This study shows that plurality-specific birthweight-by-gestation standards should be used for assessment of fetal growth in multiple births rather than singleton standards.     

Monochorionic diamniotic infants without twin-to-twin transfusion syndrome.

BACKGROUND: Monochorionic-diamniotic twins (MoDi) occur in 0.3% of all pregnancies. Twin-to-twin transfusion syndrome (TTS) that occurs in 20% of MoDi pregnancies is associated with high perinatal morbidity and mortality. MoDi twins without TTS are more frequent (80%) but have been scarcely reported. OBJECTIVE: To study perinatal morbidity and mortality of 74 MoDi twin sets without TTS and to compare it to that of 38 sets of MoDi twins with TTS. METHODS: Chorionicity was determined by gender and placental examination. Gestational age (GA) was set by sonography and pediatric examination. TTS was diagnosed clinically and by sonography, discordance was defined by twins birth weight difference > or =20%, and fetal growth restriction was determined by using a twin-specific nomogram. RESULTS: MoDi twin pregnancies without and with TTS were similar in demographics, live births, history of preeclampsia, fetal distress and cesarean delivery. They were different (p<0.01) in discordant pregnancies (36 and 79%), GA at delivery (32 and 29 weeks) intrauterine growth restriction (39 and 89%) and neonatal mortality (12 and 36%). Concordant (47 sets) and discordant (27 sets) MoDi twins without TTS were clinically similar. CONCLUSIONS: MoDi twins without TTS have high rates of birth weight discordance, fetal growth restriction, fetal distress, prematurity and cesarean delivery. Although their perinatal mortality is low, the reported occurrence and the short- and long-term impacts of fetal and neonatal morbidities warrants attention.     

Body mass index--specific weight gains associated with optimal birth weights in twin pregnancies

OBJECTIVE: To formulate maternal weight gain guidelines, by maternal pregravid body mass index (BMI) status, associated with optimal fetal growth and birth weight in twins. STUDY DESIGN: This historical cohort study was based on 2,324 pregnancies with nonanomalous, liveborn twins (4,684 infants) from Ann Arbor, Charleston, Baltimore and Miami. Rates of maternal weight gain and fetal growth were modeled using multiple regression for 0-20 weeks, 20-28 weeks and 28-38 weeks (projected as necessary), controlling for potentially confounding factors. Optimal rates of fetal growth were defined as growth between the singleton and twin 50th percentiles, and optimal birth weights were defined as between the singleton 50th percentile and twin 90th percentile at > or = 36 weeks (2,850-2,950 g). RESULTS: Optimal rates of fetal growth and birth weights were associated with rates of maternal weight gain for underweight women of 1.25-1.75 lb/wk (0.57-0.79 kg/wk) to 20 weeks, 1.50-1.75 lb/wk (0.68-0.79 kg/wk) between 20 and 28 weeks and 1.25 lb/wk (0.57 kg/wk) from 28 weeks to delivery; for normal-weight women, 1-1.5 lb/wk (0.45-0.68 kg/wk) to 20 weeks, 1.25-1.75 lb/wk (0.57-0.79 kg/wk) between 20 and 28 weeks and 1.0 lb/wk (0.45 kg/wk) from 28 weeks to delivery; for overweight women, 1-1.25 lb/wk (0.45-0.57 kg/wk) to 20 weeks, 1-1.5 lb/wk (0.45-0.68 kg/wk) between 20 and 28 weeks and 1 lb/wk (0.45 kg/wk) from 28 weeks to delivery; for obese women, 0.75-1 lb/wk (0.34-0.45 kg/wk) to 20 weeks, 0.75-1.25 lb/wk (0.34-0.57 kg/wk) between 20 and 28 weeks and 0.75 lb/wk (0.34 kg/wk) from 28 weeks to delivery. CONCLUSION: Optimal rates of fetal growth and birth weights in twins are achieved at rates of maternal weight gain that vary by period of gestation and maternal pregravid BMI status.     

孕中晚期双胎之一胎死宫内存活儿预后分析

目的:分析双胎之一胎死宫内(sIUFD)后存活儿的预后。方法:回顾分析2017年1月至2019年11月在郑州大学第三附属医院分娩的sIUFD病例58例,包括sIUFD发生孕周、胎死原因、不同孕周及不同绒毛膜性存活儿的新生儿结局及脑损伤情况,并随访其神经发育情况。结果:58例孕中晚期发生sIUFD的病例中单绒毛膜双羊膜囊双胎(MCDA)27例,双绒毛膜双羊膜囊双胎(DCDA)31例。死亡原因中脐带、胎盘异常占25.9%(15/58),胎儿发育异常占5.2%(3/58);存活儿的早产率为70.7%(41/58),其中最小孕周28+1周。与DCDA双胎组比较,MCDA双胎组分娩胎龄、出生体重、Apgar评分均较低。与孕中期比较,孕晚期发生sIUFD的早产率、MCDA双胎数及急诊剖宫产率更高,新生儿出生体重、Apgar评分更低。新生儿出生后头颅超声脑异常9例,其中新生儿脑损伤3例(5.2%,3/58),分别为2例脑软化,1例脑室内出血Ⅲ级。存活儿目前的存活率为91.4%(53/58),随访时间平均28个月,3例婴幼儿智能发育量表(CDCC)监测可疑。结论:绒毛膜性、死胎发生孕周、终止妊娠的孕周是影响妊娠结局的主要因素,需加强产前、产后神经影像学检查及远期标准化随访。     

Detecting fetal growth restriction or discordant growth in twin gestations stratified by placental chorionicity

OBJECTIVE: To use recommendations made by the Evidence-Based Medicine Working Group to determine the accuracy of sonographically estimated fetal weight to diagnose fetal growth restriction (FGR) (estimated or actual birth weight < 10% for gestational age [GA]) or discordancy in dichorionic and monochiorionic twin gestations. STUDY DESIGN: The inclusion criteria for this retrospective analysis were nonanomalous twins, reliable GA and sonographic estimate of fetal weight within 21 days of live births of both fetuses beyond 26 weeks. For likelihood ratio (LR) and odds ratio (OR), 95% confidence intervals (CIs) were calculated. RESULTS: Over 52 months, 126 twin gestations met the inclusion criteria; 29% were monochorionic and 71% dichorionic. The incidence of FGR in 1 of monochorionic twin fetuses (46%) was twice as high as in dichorionic (26%; OR 2.01; 95% CI 1.00, 4.03), but the rates of discordance > or = 20% were similar (21% vs. 18%, respectively; OR 1.26; 95% CI 0.64, 2.47). The LR (95% CI) of detecting discordant growth > or = 20% was 6.1 (2.5, 15.1) for dichorionic twins and 6.0 (1.8, 20.0) for monochorionic. The LR of identifying FGR in twin A and B in dichorionic twins was 6.3 (2.0, 19.7) and 8.7 (2.9, 26.9), respectively; the corresponding LR for monochorionic twins was 14.5 (1.9, 112.3) and 18.7 (2.6, 135.1). To determine the number of twins required for a tight confidence interval around an LR of 10, post hoc sample size calculations indicated: (1) regardless of chorionicity, attaining LR > 10 is not feasible; (2) in dichorionic twins, detection of FGR with twin A or B is not possible; and (3) about 500 monochorionic pregnancies are necessary to ensure that estimated fetal weight can accurately identify FGR. CONCLUSION: Using guidelines proposed by the Evidence-Based Medicine Working Group, at present it may not befeasible to identify aberrant growth in twins.     

A hospital-based birth weight analysis using computerized perinatal data base for a Chinese population

Objectives.?We aimed to construct birth weight-for-gestational age nomograms based on a computerized perinatal data base in a hospital-based Chinese population.

Methods.?Retrospectively collected 28,052 singleton deliveries at Women and Children's Medical Center, Guangzhou, China. Standard curves of birth weight from 27 to 43 week's gestation were computed. The nomograms included the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles and standard deviations.

Results.?79.9% pregnant women delivered between 38, 39, and 40 gestational week, and the mean birth weights are 3160, 3282, and 3388?g, respectively. Preterm birth is 5.7%. In general, male birth weights are greater than females at each gestational week. The hospital-based Chinese population birth weight is lower than that of North American and Scandinavian population.

Conclusions.?A different standard birth weight is needed for different population. A hospital-based birth weight curve by gestational week is established, which can be a useful tool to estimate intrauterine fetal growth to define SGA or LGA fetuses.     

The Relationship Between Gestational Age and Birth-Weight in Twin Pregnancy

Summary: Analysis is made of fetal growth in 563 twin pregnancies. The birth-weight of a twin is affected by the duration of pregnancy and zygosity. Intrauterine growth and weight is the same as a singleton pregnancy up to a gestational age of 32 weeks. After this stage fetal growth slows markedly. The growth curves of both twins are similar with an increasing tendency towards growth retardation in twin 2 after 39 weeks' gestation. Intrauterine growth retardation, as represented by the 10th percentile line, for twin 1 joins l,094g at 31 weeks, l,836g at 36 weeks and 2,428g at 40 weeks' gestation. The corresponding figures for twin 2 are l,131g, l,875g and 2,337g respectively.     

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.     

Estimated fetal weight in the evaluation of growth in twin gestations: a prospective longitudinal study

A prospective longitudinal study was conducted in order to determine by sonographically estimated fetal weight the patterns of fetal growth in twins. Thirty-five healthy women with normal twin pregnancies were examined every three weeks from the 15th week of gestation to delivery. Among the measurements obtained were the biparietal diameter (BPD), the abdominal circumference, and the calculated fetal weight. From 15-28 weeks, the growth velocity of the BPD and abdominal circumference remained fairly constant, with a steady increase in incremental growth. Beyond this age, we observed a slowing in growth of the BPD, while the abdominal circumference continued at a constant rate. The growth velocity of the weight steadily increased throughout pregnancy. Although greater biologic variability in weight between twin A and B was observed as gestational age progressed, the overall mean weights of twin A and B were not statistically different. We have generated a nomogram of fetal weight gain throughout pregnancy.     

Accuracy of ultrasonographic fetal weight estimation in twin pregnancies

OBJECTIVE: To compare the accuracy of fetal weight estimations between normal and growth-restricted twin and singleton pregnancies in a single tertiary center. METHODS: The computerized ultrasound database of a tertiary center was searched for all fetal weight estimations made in twin pregnancies from 2001 to 2006, which were performed up to 3 days before delivery. Accuracy was compared with a control group of singleton pregnancies at a 3:1 ratio. Estimated fetal weight was calculated by the Hadlock formula. Analyses were performed for the whole group and for pregnancies associated with fetal growth restriction and discordancy. RESULTS: The study groups included 278 twins and 834 singleton pregnancies. The twins group was characterized by a higher mean absolute percentage error compared with the singleton group (8.9% compared with 6.8%). Accuracy was lower for the second twins than for the first twins. When comparing the subgroup of fetal growth restriction, differences in sensitivity and specificity were small for singleton compared with overall twins (47.5% compared with 48.9% and 97.7% compared with 95.7%, respectively). Overall accuracy was better in the singleton group (95% compared with 88%), mainly due to relatively low accuracy in the second twin (86%). For detection of discordancy, estimated fetal weight had a sensitivity of 52%, specificity of 88%, and overall accuracy of 81%. CONCLUSION: The accuracy of the ultrasonographic estimated fetal weight seems to be lower for twin gestations than for singleton gestations, especially for second twins. These data should be considered by clinicians when making decisions based on ultrasonographic characteristics.