To determine whether age modifies the effect of the number of motile spermatozoa inseminated (NMSI) as a predictor of success in Intrauterine Insemination (IUI). This retrospective cohort study included all patients who underwent IUI at an academic infertility center between October 2004 and June 2018. The primary outcome was clinical pregnancy (CP; a gestational sac and fetal heartbeat on ultrasound). Results were analyzed by patient factors including age, NMSI, duration of infertility, and cause of infertility, along with treatment factors such as number of follicles and ovulation induction protocol. Factors associated with the odds of achieving a clinical pregnancy were analyzed using binary logistic generalized estimating equations to control for clustering effects by couple. Female age was categorized as <35 years vs. ≥35 years. Seven hundred thirty-seven couples that underwent 2062 IUI cycles for heterogeneous indications were included. The overall CP rate was 15.1% per cycle, and the cumulative CP rate per couple was 35.9%. For females < 35 years, the odds of CP per cycle were reduced for NMSI categories (× 106) of < 5.0 vs. ≥10.0 (OR = 0.49; 95% CI 0.29–0.83); the odds of CP per cycle did not differ for NMSI 5.0–9.9 vs. ≥10.0 (OR = 0.66; 0.37–1.18). For those ≥35 years, no difference was seen in the odds of CP per cycle for NMSI categories < 5.0 vs. ≥10.0 (OR = 1.55; 95% CI 0.72–3.31) or 5.0–9.9 vs. ≥10.0 (OR = 1.04; 95% CI 0.48–2.27). These results suggest that the NMSI can be used as a predictor of success in IUI in couples with women who are < 35 years of age; these patients should be counselled about their lower pregnancy rates when the NMSI is < 5.0 × 106. In patients ≥35 years, the NMSI does not appear to be a useful predictor of success. Further studies with larger sample size should be conducted.

Background: Measurement of mid-gestation cervix length has become a common screening tool for preterm birth. Our study was designed to assess the value of cervix length and serum relaxin in the prediction of spontaneous preterm birth at < 35 and < 37 weeks' gestation in a general obstetric population.Methods: A prospective cohort of women with a singleton pregnancy had blood collected at 24 and 28 weeks' gestation for determination of serum relaxin immediately before transvaginal ultrasound measurement of cervical length. Patients and referring physicians were blinded to cervix length and relaxin levels to preclude changes in management. The primary outcomes were spontaneous delivery at < 35 and < 37 weeks' gestation.Results: A total of 1004 women entered the study. Delivery data were not available for 20 women who delivered elsewhere. Twenty women were excluded because preterm delivery was undertaken because of pregnancy abnormalities. Of the 964 women with known gestational age at delivery, 46 (4.8%) delivered at < 37 weeks and 16 (1.7%) at < 35 weeks' gestation. Mean cervix length at 28 weeks (36.7 +/- 7.3 mm) was significantly shorter than at 24 weeks (37.8 +/- 7.1 mm) (P < 0.001). Cervix length at 24 and 28 weeks' gestation was equally predictive of preterm birth. A cervix length of <= 30 mm at 28 weeks had a sensitivity of 57.1%, a specificity of 81.8%, and a positive predictive value of 4.5% for birth at < 35 weeks. Serum relaxin levels were not correlated with cervix length at either 24 or 28 weeks. Serum relaxin at 24 and 28 weeks' gestation was not associated with preterm birth before or after controlling for patient characteristics and cervix length.Conclusion: Serum relaxin levels at 24 and 28 weeks' gestation are not associated with preterm birth. Although cervix length is associated with preterm birth, its positive predictive value is low. Given the lack of proven therapies for those at risk, cervix length does not appear to be a useful screening tool for preterm delivery in the general obstetric population.