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ORIGINAL RESEARCH |
* For additional members of the National Institute of Child Health and Human Development, Maternal-Fetal Medicine Units Network, see the Appendix.
From the 1Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, Texas; 2Department of Obstetrics and Gynecology, University of Alabama at Birmingham, Birmingham, Alabama; 3Department of Obstetrics and Gynecology, Thomas Jefferson University, Philadelphia, Pennsylvania; 4the Biostatistics Center, George Washington University, Rockville, Maryland; 5Department of Obstetrics and Gynecology, Wake Forest University School of Medicine, Winston-Salem, North Carolina; 6Department of Obstetrics and Gynecology, University of Utah, Salt Lake City, Utah; 7Department of Obstetrics and Gynecology, University of Cincinnati, Cincinnati, Ohio; 8Department of Obstetrics and Gynecology, University of Texas at San Antonio, San Antonio, Texas; and 9Department of Obstetrics and Gynecology, University of Tennessee, Memphis, Tennessee.
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ABSTRACT |
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 ABSTRACT MATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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METHODS: This is a secondary analysis of a multicenter, blinded observational study of endovaginal sonographic examinations performed at 16–18 weeks of gestation on 187 women with singleton gestations who were at high risk for recurrent spontaneous preterm birth (prior spontaneous preterm birth at < 32 weeks of gestation). At the time of enrollment, each woman was interviewed by a research nurse with regard to her sexual history. The patient was asked about the number of sexual partners in her lifetime, the number of sexual partners since the start of her pregnancy, and, on average, the frequency of intercourse per week in the preceding month.
RESULTS: A total of 165 pregnancies were available for this analysis. The population incidence of spontaneous preterm birth at less than 37 weeks of gestation in the study pregnancy was 36%. An increasing number of sexual partners in a woman's lifetime was associated with an increased risk of spontaneous preterm delivery (one partner 19%, 2–3 partners 29%, 
4 partners 44%, P = .007), whereas the number of sexual partners since the start of pregnancy was not (P = .42). Women who reported infrequent sexual intercourse during early pregnancy had an incidence of recurrent spontaneous preterm birth of 28% compared with 38% in those women who reported some intercourse (P = .35).
CONCLUSION: Self-reported coitus during early pregnancy was not associated with an increased risk of recurrent preterm delivery. There was an association between increasing number of sexual partners in a woman's lifetime and recurrent preterm delivery.
LEVEL OF EVIDENCE: II-2
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MATERIALS AND METHODS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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Each woman underwent a structured interview at 16.0–18 weeks and 6 days of gestation by a research nurse to obtain a record of her sexual history. The patient was asked about the number of sexual partners in her lifetime, the number of sexual partners since the start of her pregnancy, and, on average, the number of times per week the patient had intercourse in the past 4 weeks. Because this was a secondary analysis of a blinded observational study of the predictive value of serial cervical length measurements, the results of each scan were not made available to the patient's managing physician, except in cases of complete placenta previa or fetal death. Therefore, the patients were not given instructions to alter or restrict any physical activity based on the results of the ultrasound measurements.
The primary outcome of interest was preterm delivery before 37 completed weeks of gestation due to spontaneous preterm labor or preterm membrane rupture. The risk of preterm birth was analyzed with respect to the number of lifetime partners and the number of sexual partners since the start of pregnancy. The frequency of sexual intercourse was categorized into 2 groups: none or any. Categorical variables were compared by using the 
2, Fisher exact, or Mantel-Haenszel test of trend, and continuous data were compared by using the Wilcoxon rank sum test. Logistic regression was used to examine the relationship between the primary outcome and the number of lifetime sexual partners, controlling for maternal age. Data were analyzed with SAS 8.0 (SAS Institute Inc, Cary, NC). Probability values < .05 were considered significant, but no adjustments were made for multiple comparisons.
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RESULTS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIXREFERENCES |
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The mean gestational age at delivery of the study pregnancy was 35.0 ± 6.3 weeks. A total of 60 (36%) women experienced a spontaneous preterm birth before 37 weeks, 45 (27%) before 35 weeks, 31(19%) before 32 weeks, 27 (16%) before 28 weeks, and 19 (12%) before 24 weeks. An additional 8 women underwent an indicated preterm delivery at 31–36 weeks of gestation for obstetric indications. Of the 60 spontaneous births before 37 weeks, 42 (70%) were associated with preterm labor and 18 (30%) were associated with preterm membrane rupture.
The demographic and obstetric history characteristics of the women delivering spontaneously at less than 37 weeks of gestation compared with those delivering at 37 weeks or later or with an indicated delivery are shown in Table 1. There were no significant differences between the 2 groups. An increasing number of sexual partners in a woman's lifetime was associated with an increased risk of recurrent spontaneous preterm delivery (one partner 19%, 2–3 partners 29%, 4 partners 44%, P = .007 from test of trend) (Table 2), whereas the number of sexual partners since the start of pregnancy was not (
1 partner 37%, 2 partners 14%, P = .42). Patients with 3 or more sexual partners in their lifetime had an increased risk of spontaneous preterm delivery, even after controlling for maternal age (odds ratio 2.3, P = .03).
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The frequency of recurrent preterm birth was analyzed by the number of times per week the patient had intercourse in the past 4 weeks (Table 2). Because the frequency of preterm birth was nearly identical for all groups where any coitus occurred, these groups were combined and placed in the "any" group, while those women whose frequency of self-reported intercourse per week in the preceding month averaged zero were in the "none" group. Women in the entire cohort who were in the "none" group (n = 25) during early pregnancy had an incidence of recurrent spontaneous preterm birth at less than 37 weeks of 28%, compared with 38% (P = .35) in those women who reported some intercourse (n = 140). This study had a 75% power to detect a 2-fold increase in recurrent spontaneous preterm delivery (from 28% in those women in the "none" group when compared to 56% in the group reporting some sexual intercourse).
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DISCUSSION |
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In a study focusing on the role of infection in the etiology of preterm birth, Toth and colleagues4 demonstrated that 3% of women with one lifetime sexual partner had premature rupture of membranes compared with 13% in those with 2 or more lifetime sexual partners (P = .02). The authors suggested that an increased number of lifetime sexual partners might increase the risk for prepregnant asymptomatic bacterial colonization of the uterine cavity. It was hypothesized that these organisms may then proliferate because of alterations in host defense mechanisms during pregnancy and subsequently invade the fetal membranes, placenta, and amniotic fluid, resulting in pregnancy loss. Such a hypothesis may explain our findings of increased risk of recurrent spontaneous preterm birth with increasing number of lifetime sexual partners.
In a study involving over 39,000 women who were without obstetric or chronic medical conditions predisposing them to preterm delivery, Klebanoff and colleagues5 found no increased risk of preterm delivery with coitus at 28–29, 32–33, and 36–37 weeks of gestation. In another large trial involving over 13,000 low-risk women, Read and colleagues6 found that frequent intercourse (defined a priori as once per week or more) at 23–26 weeks was not associated with an increased risk of preterm birth. In fact, they demonstrated a trend of decreasing risk of preterm delivery with increasing frequency of sexual intercourse. They postulated that this inverse association was due to the relative health and lack of complications in the pregnancies of those women engaging in sexual intercourse. In contrast, Goodlin and colleagues7 found that orgasm after 32 weeks was associated with preterm delivery, while Wagner et al8 found this association in the first trimester. Brustman and colleagues9 have demonstrated a 5-fold increase in the mean frequency of contractions in the immediate postcoital period in women who had been treated for preterm labor when compared with low-risk woman. Proposed mechanisms for the association between coitus and preterm delivery include the stimulation of uterine contractions from prostaglandins in seminal fluid and the release of oxytocin from nipple stimulation and orgasm.6
Most of the information available on sex-related issues in pregnancy come from studies conducted in low-risk populations. Given that a history of a prior spontaneous preterm birth is generally accepted to be a risk factor for recurrence, we wondered if self-reported infrequent intercourse during early pregnancy might have a protective effect on preterm delivery in this high-risk group. We did not find a significant difference in delivery at less than 37 weeks of gestation between those women who reported any intercourse and those in the "none" group in early pregnancy. Therefore, our findings of no increase in preterm birth in those women reporting coitus is consistent with the preponderance of other published experiences. This study had a 75% power to detect a 2-fold increase in recurrent spontaneous preterm delivery (from 28% in those women in the "none" group when compared with 56% in the group reporting some sexual intercourse). Thus, a more modest association between intercourse and spontaneous preterm delivery cannot be ruled out.
A need exists for objective data on the impact of different forms of maternal activity during pregnancy and, specifically, the advisability of unrestricted coitus in women with prior preterm births. Our results suggest that coitus during early pregnancy may not increase the risk of recurrent preterm birth. Moreover, the association between increasing number of sexual partners in a woman's lifetime and recurrent preterm delivery suggests that prepregnancy sexual behavior may influence pregnancy outcome.
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APPENDIX |
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Footnotes |
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Corresponding author: Nicole P. Yost, MD, Emory University School of Medicine Department of Obstetrics and Gynecology, 69 Jesse Hill Jr Drive SE, Room 407, Atlanta, GA 30303; e-mail: nicolepyost{at}yahoo.com. 
doi:10.1097/01.AOG.0000206757.92602.b5
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REFERENCES |
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2. Shellhaas CS, Iams JD. Ambulatory management of preterm labor. Clin Obstet Gynecol 1998;41:491–502.[Medline]
3. Owen J, Yost N, Berghella V, Thom E, Swain M, Dildy GA, et al. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA 2001;286:1340–8.
4. Toth M, Witkin SS, Ledger W, Thaler H. The role of infection in the etiology of preterm birth. Obstet Gynecol 1988;71:723–6.
5. Klebanoff MA, Nugent RP, Rhoads GG. Coitus during pregnancy: is it safe? Lancet 1984;2:914–7.[Medline]
6. Read JS, Klebanoff MA. Sexual intercourse during pregnancy and preterm delivery: effects of vaginal microorganisms. The Vaginal Infections and Prematurity Study Group. Am J Obstet Gynecol 1993;168:514–9.[Medline]
7. Goodlin RC, Keller DW, Raffin M. Orgasm during late pregnancy: possible deleterious effects. Obstet Gynecol 1971;38:916–20.
8. Wagner NN, Butler JC, Sanders JP. Prematurity and orgasmic coitus during pregnancy: data on a small sample. Fertil Steril 1976;27:911–5.[Medline]
9. Brustman LE, Raptoulis M, Langer O, Anyaegbunam A, Merkatz IR. Changes in the pattern of uterine contractility in relationship to coitus during pregnancies at low and high risk for preterm labor. Obstet Gynecol 1989;73:166–8.
This article has been cited by other articles:
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  Sexual Activity and Risk for Recurrent Preterm Delivery Journal Watch (General), April 21, 2006; 2006(421): 7 - 7. [Full Text]
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