Adverse perinatal outcomes have been related to growth discordance in twin pregnancies—most often defined as a greater than 20% or 30% difference in birth weights. Both genetic and uteroplacental factors have been implicated. The investigators hypothesized that differing rates of maturation of transferred embryos are associated with discordant birth weights in dichorionic twin pregnancies resulting from assisted reproductive technology (ART). Participating in the study were 101 nulliparous women having dichorionic twin pregnancies that produced male-male or female-female infants. Thirty-eight conceived spontaneously without ovulation induction, and 63 followed in vitro fertilization and embryo transfer. Crown-rump length (CRL) was measured by ultrasonography at 9–11 weeks' gestation. Gestational age was estimated either from the maternal menstrual history as confirmed by ultrasound study of the larger fetus or from the day of oocyte retrieval.
Women with ART-conceived twin pregnancies were significantly older than those with spontaneous pregnancies, but the groups did not differ in other respects. No significant differences were found between spontaneous and ART-conceived twin pregnancies with respect to percentage CRL discordance, percentage birth weight discordance, or the incidence of birth weight discordance exceeding 20%. There was a significant positive correlation between percentage CRL disparity and percentage birth weight discordance in ART-conceived pregnancies, but no such correlation was evident in spontaneous pregnancies. An abnormal umbilical cord insertion was comparably frequent in spontaneous and ART-conceived dichorionic twin pregnancies. Abnormal cord insertion was associated with more frequent percentage birth weight discordance and birth weight discordance exceeding 20% in both spontaneous and ART-conceived pregnancies. No significant differences in percentage CRL discordance were found between pregnancies with and those without abnormal cord insertion.
These findings lead the investigators to conclude that, in ART-conceived dichorionic twin pregnancies, CRL disparity may be associated with birth weight discordance.
Department of Obstetrics and Gynecology, Japanese Red Cross Katsushika Maternity Hospital, Tokyo, Japan
Fetal Diagn Ther 2007;22:372–376