Length of second stage of labor and preterm birth in a subsequent pregnancy

Abstract

Background During the second stage of labor, it is plausible that the pressure of the fetal head against a completely dilated cervix may lead to changes in the cervical integrity and cervical strength lending it susceptible to premature dilation in a subsequent pregnancy. Therefore, a prolonged second stage of labor has been hypothesized to be a risk factor for cervical insufficiency and spontaneous preterm birth (sPTB). Objective To evaluate the effect that the length of second stage of labor in one pregnancy has on the risk of spontaneous preterm birth (sPTB) in a subsequent pregnancy. Study Design This was a planned secondary analysis of a large retrospective cohort study of women with two consecutive deliveries at our institution from 2005–2010. Women with a term pregnancy that reached the second stage were included; women with a prior sPTB were excluded. The primary outcome was sPTB <37 weeks. A prolonged second stage was defined as ≥3hrs. Fisher’s exact tests were used to compare categorical data. Linear and logistic regression was used to calculate odds. Results 757 women were included. The overall length of the second stage ranged from 0–7.3 hours. The sPTB rate in a subsequent pregnancy was 8.7%. There was no association between length of second stage (hours) as a continuous variable and sPTB after adjusting for confounders (aOR 0.83 [0.58–1.20]). A prolonged second stage ≥3hrs occurred in 48 (6.3%) women. Women with a second stage ≥3hours were older, less likely to be African American, and were less likely to be overweight or obese as compared to women with a second stage <3 hours. The women with second stage ≥3 hours were more likely to be nulliparous and have a larger neonate. The sPTB risk was not different between a second stage ≥3hrs (10.4%) and <3hrs (7.9%), p=0.5. The sPTB risk was; however, modified by mode of delivery in the second stage. There was no difference in sPTB rate among women with a vaginal delivery when comparing those with and without a prolonged second stage (7.4 vs. 7.8%, p=0.9). There also was no difference among women with a cesarean when comparing those with and without a prolonged second stage (11.8 vs. 14.3%, p=0.8). While not statistically significant, the absolute risk of a subsequent sPTB after a cesarean delivery with a second stage ≥3hrs is twice as high as the risk of a sPTB after a vaginal delivery with a second stage ≥3hrs (OR 2.08 [0.32–13.78]). Conclusions A prolonged second stage of labor alone does not increase the risk of sPTB in a subsequent pregnancy. Cesarean delivery after a prolonged second stage of labor may confer a possible increased risk. It is important to continue to evaluate potential risk factors for sPTB. If these risk factors are confirmed in future studies, it will aid in the counseling of women and may open the door for therapeutic strategies to be studied among these newly identified “at-risk” women.

Cesarean in the second stage: a possible risk factor for subsequent spontaneous preterm birth

“…First, prolonged second stage has been evaluated as a possible risk for subsequent SPTB. The first study reported an association, 4 whereas subsequent larger studies 5–7 failed to find such a link; the current study by Wood et al 1 confirms that, overall, there does not seem to be a consistent association between prolonged second stage (or the length of the second stage in general) in the prior pregnancy and subsequent SPTB. 4–7 …”

“…7 This is an important analysis because it reinforces the fact that it does not seem that prolonged second stage per se increases the future risk of SPTB, but if a CD is done in the second stage, and perhaps even more significantly, with a prolonged second stage, the risk of subsequent SPTB is increased compared with a vaginal delivery.…”

“…4,7 It has been reported that cervical trauma such as excision of cervical tissue 9,10 or uterine evacuation for abortion 2 is associated with an increased risk of subsequent SPTB.…”

“…This might happen in particular if the uterine incision in a fully dilated woman might not happen truly in the lower uterine segment, but in the cervix instead, and perhaps at the level of the internal os. 7 …”

“…7 Structural damage to the area of what is the internal os might also occur from an impacted fetal head and subsequent difficult extraction.…”