Optimal Pregnancy Spacing Interval
The optimal interpregnancy interval for preventing adverse perinatal outcomes is 18-23 months, making option B (18-60 months) the correct answer, though the lower end of this range (18-23 months) represents the ideal target.
Evidence-Based Recommendations
Primary Recommendation: 18-23 Month Interval
The strongest evidence supports an interpregnancy interval of 18-23 months as optimal for maternal and infant health outcomes 1, 2, 3. This interval is defined as the time between a live birth and the beginning of the next pregnancy (not between deliveries) 3.
Key findings supporting this interval:
- Infants conceived 18-23 months after a previous live birth demonstrate the lowest risks of preterm birth, low birth weight, and small for gestational age 3
- This association persists even after controlling for 16 biologic, sociodemographic, and behavioral risk factors 3
- A 2023 systematic review of 129 studies involving nearly 47 million pregnancies confirmed these J-shaped relationships between birth spacing and adverse outcomes 1
Risks of Short Intervals (<18 months)
Interpregnancy intervals shorter than 18 months are associated with significantly increased risks 2, 3:
- Intervals <6 months carry odds ratios of 1.40 for preterm birth, 1.61 for low birth weight, and 1.26 for small for gestational age compared to the 18-23 month reference 2
- Short intervals (<6 months) also increase risks of fetal malposition (OR 3.84), fetal growth restriction (OR 2.06), and hypertension (OR 1.86) 4
- The Society for Maternal-Fetal Medicine notes that interpregnancy intervals shorter than 6 months are associated with increased risks of preterm birth, low birth weight, and small for gestational age infants 5
Risks of Long Intervals (≥60 months)
Intervals of 60 months or longer also demonstrate increased risks 1, 2, 3:
- Long intervals (≥60 months) are associated with increased risks of preterm labor (OR 3.82), oligohydramnios (OR 2.54), gestational diabetes (OR 2.19), and anemia (OR 1.45) 4
- Infants conceived 120 months or more after a live birth have odds ratios of 2.0 for low birth weight, 1.5 for preterm birth, and 1.8 for small for gestational age 3
- Long intervals are specifically associated with increased risk of preeclampsia and gestational diabetes 1
Special Populations
After Preterm Birth
For women with a previous preterm birth, the optimal interpregnancy interval may be as short as 9 months 1. Dose-response analyses indicate that a 9-month interval after preterm birth is not associated with increased risk of recurrent preterm birth 1.
After Bariatric Surgery
Women who have undergone bariatric surgery should postpone pregnancy until stable weight is achieved, typically 1 year after sleeve gastrectomy or Roux-en-Y gastric bypass, and 2 years after adjustable gastric banding 5. This recommendation differs from general pregnancy spacing as it addresses the unique metabolic considerations following weight loss surgery 5.
Clinical Implementation
Contraceptive Counseling
Contraceptive counseling should begin early in pregnancy and continue throughout the prenatal period 5. The Society for Maternal-Fetal Medicine recommends that this counseling be patient-centered and provided in a shared decision-making framework 5.
Long-acting reversible contraception (LARC) should be offered to facilitate optimal birth spacing 5. LARC methods have superior efficacy in preventing unintended and close-interval pregnancies compared with short-acting methods 5.
Risk Assessment
Women with short interpregnancy intervals, particularly those older than 35 years, face increased morbidity and mortality risks 5. The postpartum period is especially vulnerable, as 70% of pregnancies occurring within 1 year of delivery are unplanned 5.
Common Pitfalls
- Confusing interpregnancy interval with interdelivery interval: The interpregnancy interval is measured from delivery to conception of the next pregnancy, not from delivery to delivery 3
- Failing to account for special populations: Women with previous preterm birth may safely conceive earlier (9 months) than the general recommendation 1
- Inadequate postpartum contraceptive planning: Discussion about immediate postpartum contraception should occur during the prenatal period to ensure optimal spacing 5
- Not recognizing that three-fourths of women have intervals less than the WHO-recommended minimum of 24 months: This highlights the need for increased awareness and availability of contraceptive choices 4