The Effect of Maternal Habitus on Twin Growth and Evaluation of Fetal Anatomy
This will be a prospective observational study of twin gestations that present for prenatal care in the Parkland Heath and Hospital System. Once they are enrolled for prenatal care, they will be followed in the Obstetric Complications clinic at Parkland Memorial Hospital for the remainder of their pregnancy. These pregnancies will be entered into a newly formed twin database, and maternal and fetal information will be collected throughout the gestation. Clinically obtained data points include prepregnancy maternal BMI, maternal weight at each prenatal visit, maternal tricep skinfold thickness at the first prenatal visit, the birth weight of each twin, and the finding of any major or minor anomalies identified after birth. Ultrasound parameters that will be assessed include estimated fetal weight every 4 to 6 weeks throughout the pregnancy, visualization of fetal anatomy, findings of a targeted ultrasound examination looking specifically for fetal anomalies at 18 to 22 weeks gestation, and the distance from maternal skin to the amniotic cavity at several standardized locations.
With twin gestations, there are two infants whose size may be correlated with the mother?s pregnancy weight. We would like to establish a significant association between mother?s weight and the weights of both of the twins. Consequently, our desire is not to provide evidence that the correlation between the mothers and their offspring is different from no correlation, but that it is significantly greater that some positive correlation providing a minimal degree of correlation. Hence, for statistical power we would like to provide enough evidence to recognize that a correlation of at least 0.35 (alternative) is different from that of o.15 (null, note not the usual 0.0). To do this with 80% power for a two-sided hypothesis of significance level 0.05 requires 173 deliveries. However, we have two hypothesis to address (the smallest and the largest twin), so the significance level should be 0.025 rather than 0.05, requiring 210 deliveries for 80% power. We observe about 160 twin gestation deliveries per year at Parkland Hospital, requiring about 16 months to accrue 210 deliveries. In order to capture all of the ultrasound and delivery data from the last acquired pregnancy, we will need an additional 6 months, making the total from initial accrual through the last delivery approximately 22 months of data collection.
Inclusion criteria include maternal ages 16-45 years old and all dichorionic and monochorionic/diamniotic twin gestations who present prior to 22 weeks gestation