Epidemiological studies of vacuum extraction delivery : incidence, risk factors and subsequent childbearing

Abstract

The aim of this thesis was to bring focus on factors and outcomes associated with vacuum extraction delivery (VE). Delivery by VE is associated with both maternal risks (such as obstetric anal sphincter ruptures, postpartum hemorrhage and a negative birth experience) and infant risks (such as scalp lacerations, cephalohematoma, intracranial hemorrhage and brachial plexus injury). In Sweden, every seventh first time mother is delivered by VE, yet little is known about risk factors, incidence over time, birth experience and subsequent childbearing.

In study I we used the Medical Birth Register (MBR) to investigate factors related to VE and use over time among 589 108 primiparous women with singleton, term births in 1992-2010. We found that rates of VE increased from 11.5% in 1992 to 14.8% in 2010. The risk of VE increased with maternal age and gestational length, but decreased with increasing maternal height. Logistic regression analyses showed that the increased use of VE over time was partly explained by increasing maternal age and increased use of epidural anesthesia (EDA). Among women with and without EDA, the increase in VE over time was confined to VE due to the indication non-reassuring fetal status.

In study II we included a total of 265 456 singleton neonates born to nulliparous women at term between 1999 and 2008. Compared with women giving birth to a neonate with average size head circumference (35 cm), women giving birth to an infant with a very large head circumference (39–41 cm) had significantly higher odds of being diagnosed with prolonged labor (OR 1.49, 95% CI 1.33–1.67), signs of fetal distress (OR 1.73, 95% CI 1.49– 2.03) and maternal distress (OR 2.40, 95% CI 1.96–2.95). The odds ratios for VE and cesarean section were thereby elevated to 3.47 (95% CI 3.10–3.88) and 1.22 (95% CI 1.04– 1.42), respectively.

In study III, 3006 women were interviewed in their third trimester and one month after first childbirth to assess fear of birth and birth experience. Logistic regression was performed to examine the interactions and associations between fear of birth, mode of delivery and birth experience. Compared to women with low levels of fear of birth, women with higher levels of fear had a more negative birth experience and were more affected by an EmCS or VE. Compared to women with low levels of fears with a SVD, women with high levels of fear who were delivered by VE had a 10-fold increased risk of reporting a negative birth experience (OR 10.35, 95% CI 5.25-20.39). A SVD was associated with the most positive birth experience among the women in this study.

In study IV we used a cohort of 771 690 women who delivered their first singleton infant in Sweden between 1992 and 2010 to investigate the relationship between mode of first delivery and probability of subsequent childbearing. Using Cox’s proportional-hazards regression models, risks of subsequent childbearing were compared across four modes of delivery. Compared with women who had a SVD, women who delivered by VE were less likely to have a second pregnancy (HR 0.96, 95% CI 0.95–0.97), and the probabilities of a second childbirth were substantially lower among women with a previous EmCS (HR 0.85, 95% CI 0.84–0.86) or an elective caesarean section (HR 0.82, 95% CI 0.80–0.83). There were no clinically important differences in the median time between first and second pregnancy by mode of first delivery.