Pregnancy loss managed by cervical dilatation and curettage increases the risk of spontaneous preterm birth.

STUDY QUESTION: Do women with a previous miscarriage or termination of pregnancy have an increased risk of spontaneous preterm birth and is this related to previous cervical dilatation and curettage?

SUMMARY ANSWER: A single previous pregnancy loss (termination or miscarriage) managed by cervical dilatation and curettage is associated with a greater risk of SpPTB.

WHAT IS KNOWN ALREADY: Miscarriage affects ∼20% of pregnancies and as many as a further 20% of pregnancies undergo termination.

STUDY DESIGN, SIZE, DURATION: We utilized data from 5575 healthy nulliparous women with singleton pregnancies recruited to the Screening for Pregnancy Endpoints (SCOPE) study, a prospective cohort study performed between November 2004 and January 2011.

PARTICIPANTS/MATERIALS, SETTING, METHODS: The primary outcome was spontaneous preterm birth (defined as spontaneous preterm labour or preterm premature rupture of membranes (PPROM) resulting in preterm birth <37 weeks' gestation). Secondary outcomes included PPROM, small for gestational age, birthweight, pre-eclampsia and placental abruption.

MAIN RESULTS AND THE ROLE OF CHANCE: Women with previous pregnancy loss (miscarriage or termination) were compared with those with no previous pregnancy loss. There were 4331 (78%) women who had no previous pregnancy loss, 974 (17.5%) who had one early previous pregnancy loss, 249 (4.5%) who had two and 21 (0.5%) who had three or four losses. Women with two to four previous losses, but not those with a single loss, had an increased risk of spontaneous preterm birth (adjusted OR 2.12; 95% CI 1.55, 2.90) and/or placental abruption (adjusted OR 2.30; 95% CI 1.36, 3.89) compared with those with no previous pregnancy. A single previous miscarriage or termination of pregnancy where the management involved cervical dilatation and curettage was associated with an increased risk of spontaneous preterm birth (adjusted OR 1.64; 95% CI 1.08, 2.50; 6% absolute risk and adjusted OR 1.83; 95% CI 1.35, 2.48; 7% absolute risk, respectively) compared with those with no previous pregnancy losses. This is in contrast with women with a single previous miscarriage or termination managed non-surgically who showed no increase risk (adjusted OR 0.86; 95% CI 0.38, 1.94; 3.4% absolute risk and adjusted OR 0.87; 95% CI 0.69, 1.12; 3.8% absolute risk, respectively).

LIMITATIONS, REASONS FOR CAUTION: Although every effort was made to record accurate previous pregnancy data, it was not feasible to confirm the history and management of previous pregnancy loss by hospital records. This may have introduced recall bias.

WIDER IMPLICATIONS OF THE FINDINGS: This large prospective cohort study of healthy nulliparous women has demonstrated that women with either a previous miscarriage or termination of pregnancy were at increased risk of spontaneous preterm birth if they were managed by procedures involving cervical dilatation and curettage. However, overall, women with a single pregnancy loss did not have an increased risk of having any other of the adverse pregnancy outcomes examined. In contrast, two to four previous pregnancy losses were associated with an increased risk of having a pregnancy complicated by spontaneous preterm birth and/or placental abruption. Research is required to determine whether non-surgical management of miscarriage or termination of pregnancy should be advocated over surgical treatment.

STUDY FUNDING/COMPETING INTEREST(S): New Zealand: New Enterprise Research Fund, Foundation for Research Science and Technology; Health Research Council; Evelyn Bond Fund, Auckland District Health Board Charitable Trust. Australia: Premier's Science and Research Fund, South Australian Government. Ireland: Health Research Board. Leeds: Cerebra Charity, Carmarthen. Manchester: National Health Service NEAT Grant; Manchester Biotechnology and Biological Sciences Research Council; University of Manchester Proof of Concept Funding. King's College London: Guy's and St Thomas' Charity. King's College London and Manchester: Tommy's-The Baby Charity.

TRIAL REGISTRATION NUMBER: N/A.