Objective
We sought to compare rates of recurrent spontaneous preterm birth (SPTB) in women receiving 17-α-hydroxyprogesterone caproate (17P) with prior SPTB due to preterm labor (PTL) vs preterm premature rupture of membranes (PPROM).
Study Design
Women with singleton gestation having 1 prior SPTB enrolled at 16-24.9 weeks’ gestation for weekly outpatient 17P administration were identified from a database. Rates of recurrent SPTB were compared between those with prior SPTB due to PTL or PPROM overall and by gestational age at prior SPTB.
Results
Records from 2123 women were analyzed. The prior PTL group vs the prior PPROM group experienced higher rates of recurrent SPTB at <37 weeks (29.7% vs 22.9%, P = .004), <35 weeks (14.0% vs 9.1%, P = .004), and <32 weeks (5.9% vs 3.3%, P = .024), respectively.
Conclusion
Reason and gestational age of prior SPTB influence the likelihood of recurrent SPTB in women receiving 17P prophylaxis.
Preterm birth (PTB) remains a leading cause of infant morbidity and mortality. Approximately 40-45% of preterm deliveries are due to spontaneous preterm labor (PTL), and 25-30% are preceded by preterm premature rupture of membranes (PPROM). Women with a history of PTB due to either PTL or PPROM are at risk for recurrent preterm delivery in a subsequent pregnancy. Previous investigators have reported that overall, women with a prior spontaneous PTB (SPTB) for either reason carry a 2.5-fold increase in risk for SPTB recurrence in a subsequent pregnancy. A history of SPTB due to PTL carries a 2.2-fold increase in risk for SPTB in a current pregnancy, while a history of SPTB due to PPROM carries a 3.3-fold increase in risk for PTB recurrence. These reported risk ratios are far from consistent though, as other investigators have reported both higher and lower recurrence rates.
Administration of 17-α-hydroxyprogesterone caproate (17P) as a prophylactic treatment for prevention of recurrent SPTB has been widely adopted in clinical practice without regard to whether the prior PTB was related to PTL or PPROM. We sought to evaluate if rates of recurrent SPTB are different in women whose prior PTB was due to PTL or due to PPROM.
Materials and Methods
We conducted a retrospective analysis of deidentified data collected from 2006 through 2009 from high-risk pregnant women prescribed weekly 17P injections for prophylactic prevention of recurrent PTB. Weekly 17P injections were administered in the patient’s home by a nurse employed by the Division of Women’s and Children’s Health, Alere Health. The 17P home administration program was prescribed by each woman’s physician and was in addition to routine prenatal care. Clinical data were prospectively collected by Alere nurses from the patient and her physician and entered into a relational database throughout provision of homecare services and after delivery. At initiation of outpatient services all women gave written consent for nursing care and allowed the use of their deidentified protected health information for research and reporting purposes. Only deidentified data, deemed exempt from institutional review board approval, were used in completion of this study.
The outpatient program includes individual patient education provided by a perinatal nurse on the signs and symptoms of PTL, weekly home nursing visits with clinical assessment, and nurse-administered compounded 17P injections (250 mg intramuscularly). In addition to weekly nursing assessments and 17P injections, patients had access to telephonic perinatal nursing and pharmacist support 24 hours a day, 7 days a week for any pregnancy-related concerns.
From eligible patient records, those meeting the following criteria were identified: current singleton gestation, history of 1 PTB, and documentation of gestational age and reason for prior PTB (either PTL or PPROM). Women having an indicated prior preterm delivery, >1 prior preterm delivery, or cerclage in the current pregnancy were excluded. Included for analysis were women initiating 17P in the current pregnancy between 16-24.9 weeks’ gestation having a documented pregnancy outcome.
Study groups were determined by patient-reported reason for prior PTB: PTL (n = 1639) or PPROM (n = 448). PTL was defined as labor occurring <37 weeks of gestation resulting in PTB. PPROM was defined as prelabor rupture of membranes occurring <37 weeks of gestation. Other information such as latency from PPROM to delivery and treatments received to forestall delivery in the prior PTB were not available from the outpatient record of the current pregnancy. Within each PTL or PPROM group, 3 subgroups were identified by the gestational age of the prior PTB (20-27.9, 28-33.9, or 34-36.9 weeks). Pearson χ 2 was used to compare rates of recurrent SPTB between those with prior PTB due to PTL or due to PPROM overall and within each gestational age at prior PTB group. Two-sided P values < .05 were considered statistically significant. Logistic regression was used to evaluate the influence of PTL or PPROM history and maternal characteristics with a P < .10 on the primary study outcome. The primary study outcome was the rate of recurrent SPTB.
Results
Records from 2123 women were analyzed; 1639 (77.2%) with a prior SPTB due to PTL and 484 (22.8%) due to PPROM. Maternal characteristics are presented in Table 1 . Women with prior PTL were younger, less likely to be married, and initiated 17P at a slightly greater gestational age than women with prior PPROM. Important risk factors for PTB, maternal African American race and smoking, were similar between the groups. While the gestational age of prior PTB was similar overall, differences were observed in the distribution of gestational ages. Women with prior PTL had a greater incidence of prior PTB between 20.0-27.9 weeks, while those with prior PPROM had a greater incidence of prior PTB between 28.0-33.9 weeks. Rates of early PTB between 20.0-23.9 weeks were similar between the PTL and PPROM groups at 5.6% and 5.0%, respectively ( P = .612).
| Characteristic | SPTB-PTL (n = 1639) | SPTB-PPROM (n = 484) | P value | OR (95% CI) |
|---|---|---|---|---|
| Gravidity | 3.0 ± 1.4 | 3.0 ± 1.2 | .512 | — |
| 3 (2, 12) | 3 (2, 9) | |||
| Only 1 prior SPTB | 100% | 100% | N/A | — |
| History of ≥1 term birth | 6.6% | 5.0% | .192 | — |
| Married | 73.9% | 80.0% | .007 | 0.71 (0.55–0.91) |
| Maternal race | ||||
| African American | 17.2% | 14.7% | .188 | — |
| Caucasian | 76.1% | 78.3% | .323 | — |
| Asian | 3.2% | 2.9% | .706 | — |
| Other | 3.4% | 4.1% | .457 | — |
| Smoker | 5.4% | 3.3% | .065 | — |
| Maternal age, y | 30.2 ± 5.4 | 32.0 ± 5.1 | < .001 | — |
| 30 (17, 46) | 32 (19, 45) | |||
| Age <20 y | 1.1% | 0.6% | .501 | — |
| Age ≥35 y | 23.2% | 31.4% | < .001 | 0.66 (0.53–0.82) |
| GA 17P start, wk | 18.8 ± 2.5 | 18.5 ± 2.4 | .043 | — |
| 17.9 (16, 24.9) | 17.6 (16, 24.9) | |||
| Initiated 17P at <21 wk | 79.1% | 82.2% | .128 | — |
| Prior GA at delivery, wk | 31.4 ± 4.2 | 31.4 ± 3.7 | .095 | — |
| 33 (22, 36) | 32 (22, 36) | |||
| 20.0-27.9 | 22.0% | 16.1% | .005 | 1.47 (1.12–1.92) |
| 28.0-33.9 | 35.6% | 45.0% | < .001 | 0.67 (0.55–0.83) |
| 34.0-36.9 | 42.5% | 38.8% | .156 | — |
| 20.0-23.9 | 5.6% | 5.0% | .612 | — |
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