Sonographic growth curves of triplet conceptions

Is it normal for multiples to be smaller than singletons?

This section discusses fetal growth in multiple pregnancy from various perspectives. Whereas the entire 'fetal mass' of a multiple pregnancy can exceed the 90th birth weight percentile of a singleton of the same gestational age, the individual fetuses might exhibit growth patterns compatible with adaptation to the limited uterine environment. Adaptation can take the form of relative growth restriction (i.e. discordance), whereby not all fetuses show a decelerating growth pattern. When adaptation fails, fetal growth is genuinely restricted. However, even in cases with significant discordance, about 40% of the smaller twins weigh above the 10th birth weight percentile. The key in these circumstances might be found in the ability to recognize the transition from the physiologic adaptation into the pathologic process of growth restriction.

Comprehensive fetal ultrasonographic growth measurements in triplet gestations

OBJECTIVE

Our purpose was to create tables and graphs of ultrasonographically derived fetal growth parameters in longitudinally studied triplet gestations from a single center.

STUDY DESIGN

All triplet pregnancies managed by our division from 1987 through 1998 were identified. All had first-trimester dating sonograms and complete obstetric sonograms obtained by means of 3.5- or 5.0-MHz curvilinear transducers with freeze-freeze capability and on-screen calipers. Sonograms to assess fetal growth were obtained every 2 to 4 weeks, from 16 to 18 weeks' gestation until delivery. Fetal parameters obtained with each sonogram included biparietal diameter; head circumference; bicerebellar diameter; abdominal circumference; femur, humerus, tibia, and fibula lengths; estimated fetal weight; and head circumference/abdominal circumference ratio. Regression analysis was performed with JMP and Cricket Graph software packages, and lines of best fit with 95% confidence intervals were generated.

RESULTS

A total of 443 ultrasonographic examinations were performed for 33 triplet pregnancies (99 fetuses). Each had between 3 and 6 sonograms obtained, all between 16 and 35 weeks' gestation. Scatterplots of each of the fetal growth parameters against gestational age were created with regression lines of best fit and 95% confidence intervals. All growth parameters were dependent on gestational age.

CONCLUSION

A comprehensive set of fetal growth measurements in triplets from the United States is now available and can be used to assess longitudinal fetal growth.

Fetal growth in multifetal gestation

Multiple gestations present a significant increase in fetal growth abnormalities in direct relationship to the number of fetuses present. Various definitions of birth weight discordancy exist (> or = 15%-40%). When first trimester discordancy in CRL or gestational sac diameter or early second trimester discordancies of BPD, HC, AC, or femur length are detected, genetic counseling and further work-up, including chromosomal analysis, should be considered. AC and SEFW are the best sonographic predictors of second and third trimester growth discordancy of twins. Discordant Doppler velocimetry of the umbilical arteries enhances ultrasonographic diagnosis of twin discordancy. Karyotyping also should be considered on second or third trimester diagnosis of growth discordancy. Twin-twin transfusion should be considered when growth discordancy is diagnosed in monochorionic gestations. Concordant twins with appropriate-for-gestational-age growth parameters should be followed with repeated sonographic assessment of fetal growth at approximately 4-week intervals. Discordant twins should be followed by repeat sonographic assessment of fetal growth at closer intervals, most probably every 2 weeks. Surviving singleton fetuses, after spontaneous fetal death of a twin at > 16 weeks of gestation, should be followed with antepartum surveillance similar to that of discordant twins. In rare cases of extremely premature twins with discordant growth and deteriorating fetal well-being of the growth-restricted twin, conservative management should be considered in favor of the normally grown fetus.