ORLANDO – Short cervical length during the first trimester predicts preterm delivery of an in vitro fertilization pregnancy, according to two retrospective studies involving a total of 167 women.
Although they used slightly different parameters, researchers who assessed 113 women at Montreal Fertility Center and others who studied 54 women at Detroit Medical Center reached the same conclusion: A cervical length shorter than approximately 4 cm is associated with greater risk of delivery before 37 weeks' gestation.
These studies are part of a move to identify women at risk for preterm delivery earlier, when clinicians would have more time to intervene. Some previous researchers report associations between shorter midterm cervical length and preterm delivery (Ultrasound Obstet. Gynecol. 2008;32:640-5), while others point to a need for additional evidence (Cochrane Database Syst. Rev. 2009;CD007235 [doi:10.1002/14651858.CD007235.pub2]).
“Little is known about the predictive value of a first-trimester cervical length measurement,” Dr. Olivia Vincent-Boulay of the Montreal Fertility Centre said at the meeting.
Dr. Vincent-Boulay and her associates reviewed transvaginal ultrasound findings for 113 women who conceived via in vitro fertilization (IVF) at their center. Cervical length measurements were taken between 6 and 12 weeks' gestation. A total 60% delivered full term, at 37 weeks or longer. Another 23% delivered at 34-36 weeks; 10% at 30-33 weeks; and 7% of women delivered before 30 weeks' gestation. Thus, 40% delivered prior to 37 weeks' gestation.
As their average first-trimester cervical length decreased, so did mean gestational age. For example, women with a cervix of 5 cm or longer delivered at a mean of 37 weeks. This decreased to 35 weeks for those with a cervical length from 4.0 cm to 4.9 cm and to 32 weeks for mothers with a cervix shorter than 4.0 cm.
“Our sample size was pretty small, which is why we chose 5-cm and below 4-cm groups,” Dr. Vincent-Boulay said. “It would be great to do further studies with a larger sample to do a more stratified analysis.”
There were some interesting differences between the 86 singleton and 27 twin pregnancies. Cervical length below 5 cm during the first trimester significantly correlated with preterm delivery in twin pregnancies. In the case of singletons, only a measurement below 4 cm was a significant predictor. The researchers assessed serial ultrasound measurements, and found, for example, that cervical length at 10 weeks predicted a preterm delivery of twins but not singletons.
Of the 113 IVF pregnancies, 86 or (76%) were singletons and 27 (24%) were twins. A greater number of singletons were delivered at full term (58 children), compared with twins (10 sets) in the study.
Put into clinical terms, Dr. Vincent-Boulay said: “Less than 4 cm at any time during pregnancy, whether it is single or twins, may be a cause for alarm. A cervical length less than 5 cm at 10 weeks for twins is also significant risk for preterm delivery.”
A second study presented at the ASRM meeting revealed a very similar cervical length cutoff during the first trimester, 38.5 mm (or 3.85 cm) or less. Dr. Zain Al-Safi and his colleagues reviewed the records for 54 women who conceived via IVF at Wayne State University/Detroit Medical Center.
Specifically, they found 17 or 32% of pregnant women with a short cervical length measured at the first ultrasound (between 5 and 9 weeks' gestation) delivered before 37 weeks' gestation. Fifteen women who delivered preterm had an ultrasound measurement of 38.5 mm or less, giving this cutoff a sensitivity of 47% and a specificity of 81%.
This study is important because “premature delivery is a major obstetric complication and a substantial contributor to neonatal morbidity,” said Dr. Al-Safi, an ob.gyn. at Wayne State University.
A total 21 women (39%) had multiple gestations. A meeting attendee commented that this was a high percentage and asked about IVF embryo transfer protocol.
“We did not include that in our results. We looked at twins, but did not go back and look at how many embryos were transferred,” Dr. Al-Safi replied.
A follow-up question was asked about the findings without multiples. “We took out multiples and frozen embryos and found similar results,” Dr. Al-Safi said.
A lack of follow-up ultrasound assessment in the second trimester, a small sample size, and the retrospective design are potential limitations, Dr. Al-Safi said. The findings should be considered experimental until replicated in larger, prospective studies, he added.
“If we know cervical length in the future correlates to preterm delivery … we could prevent it,” Dr. Al-Safi said.
Future studies also should evaluate the optimal management for patients with a short cervix, Dr. Vincent-Boulay said.