Objective
Cervical collagen concentration decreases during pregnancy. The increased risk of preterm birth after a short interpregnancy interval may be explained by an incomplete remodeling of the cervix. The objective of this study was to describe the changes in cervical collagen concentration over 15 months after delivery.
Study Design
The collagen concentrations were determined in cervical biopsy specimens that were obtained from 15 women at 3, 6, 9, 12, and 15 months after delivery.
Results
The mean cervical collagen concentrations were 50%, 59%, 63%, 65%, and 65% of dry weight (SD, 4.2–6.5). This increase was statistically significant until month 9, but not between months 9 and 12.
Conclusion
Low collagen concentrations in the uterine cervix may contribute to the association between a short interpregnancy interval and preterm birth.
A short interpregnancy interval (the interval between birth and a subsequent conception) is associated with an increased risk of preterm birth. Thirty original studies that provided data on preterm birth and interpregnancy interval were included in a metaanalysis from 2006. The metaanalysis included only studies that had been adjusted for at least maternal age and socioeconomic status. With interpregnancy intervals of <6 months, the adjusted odds ratio was 1.40; with interpregnancy intervals between 6 and 17 months, the adjusted odds was 1.11.
The causal mechanism is unknown but could be associated to nutritional depletion by pregnancy because inadequate stores of nutrients are associated with an increased risk of preterm birth. In particular iron and folate stores may require >6 months to be repleted after a pregnancy. Women with short interpregnancy intervals may not have had sufficient time to replenish their nutritional stores. Studies on associations between maternal nutritional depletion and preterm birth, however, do not reveal clear evidence.
Another causal mechanism might be an incomplete remodeling of the cervix after birth. During pregnancy, the cervical collagen concentration decreases by 45–75%, compared with nonpregnant values. This decrease is thought to be a prerequisite for a vaginal delivery. Thus, a relatively high cervical collagen concentration during labor is associated with prolonged duration of cervical dilation. Because the remodeling of the cervical collagen after birth has never been described, the aim of this study was to describe how the cervical collagen concentration changes during the first 15 months after birth.
Materials and Methods
The study population consisted of 15 white women with uncomplicated pregnancies ( Table 1 ). Two to 3 biopsy specimens (2 × 2–3 mm) were obtained from the ectocervix at least 5 mm from the external os from each woman at 3, 6, 9, 12, and 15 months after delivery by means of biopsy forceps (3 × 7 mm cup; Tischler-Morgan; HBH Medizintechnik GmbH, Tuttlingen, Germany). With the exceptions of slight vaginal bleeding, there were no complications that resulted from the sampling procedure.
| Characteristic | Measurement |
|---|---|
| Maternal age, y a | 28.3 ± 3.2 |
| Pregnancies, n (%) | |
| Primigravid | 6 (40) |
| Multigravid | 9 (60) |
| Births, n (%) | |
| Primiparous | 10 (67) |
| Multiparous | 5 (33) |
| Gestational age, d a | 278 ± 12 |
| Induction of labor with prostaglandin, n (%) | 1 (7) |
| Breastfeeding, n (%) | |
| <3 mo | 4 (33) |
| 3-5 mo | 2 (13) |
| 6-8 mo | 7 (47) |
| >8 mo | 2 (13) |
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