Use effective contraception once sexual intercourse resumes postpartum, as breastfeeding is not reliable birth control; wait at least 18 months before conceiving the next child

Ovulation can resume as early as 3 weeks postpartum, even while nursing and before menstruation returns. Lactational amenorrhea method (LAM) prevents over 99% of pregnancies only if three strict conditions are simultaneously met: exclusive breastfeeding, complete absence of menses, and infant under 6 months. If any condition lapses, another birth control method is essential. Conceiving less than 6 months after delivery increases preterm birth risk by approximately 40%; the World Health Organization recommends waiting at least 18 to 24 months before conceiving again.

Condoms cost a few dollars per box. Subdermal implants or IUD placement require an outpatient clinic visit. The challenge is remembering to manage contraception amid the exhaustion of newborn care.

The UK NHS states pregnancy is possible 3 weeks after childbirth. A meta-analysis of 67 studies evaluating birth spacing found that interpregnancy intervals under 6 months (measured from prior birth to next conception) were associated with a 40% increased risk of preterm birth (OR 1.40, 95% CI 1.24–1.58), a 61% increase in low birth weight (OR 1.61, 95% CI 1.39–1.86), and a 26% increase in small-for-gestational-age infants (OR 1.26, 95% CI 1.18–1.33) compared to intervals of 18–23 months. A Canadian cohort study of 148,000 pregnancies comparing 6-month vs. 18-month intervals showed that among mothers aged 35 and older, maternal severe morbidity or mortality was 0.62% vs. 0.26% (adjusted risk ratio aRR 2.39, 95% CI 2.03–2.80); for infants of mothers aged 20–34, adverse perinatal outcomes were 2.0% vs. 1.4% (aRR 1.42, 95% CI 1.36–1.47). The World Health Organization recommends a minimum interpregnancy interval of 24 months (and at least 6 months following a miscarriage or induced abortion) to allow maternal physiological and micronutrient replenishment.

Controversy: Optimal intervals remain debated between 18 and 24 months, with NHS recommending at least 12 months. An Australian within-mother matched sibling cohort study suggested that part of the short-interval risk may stem from unmeasured maternal socioeconomic factors (within-mother OR 1.07 for preterm birth). However, the necessity of proactive contraception itself is uncontroversial. Barrier condoms and progestin-only implants can be initiated immediately postpartum, while combined oral contraceptives should generally wait until at least 6 weeks postpartum if breastfeeding. Discuss contraceptive selection during the routine 42-day postpartum examination (Chapter 27, Rule 16).

NHS. Sex and contraception after birth. https://www.nhs.uk/baby/support-and-services/sex-and-contraception-after-birth/；NHS. Natural family planning. https://www.nhs.uk/contraception/methods-of-contraception/natural-family-planning/；Conde-Agudelo A, Rosas-Bermúdez A, Kafury-Goeta AC (2006). Birth spacing and risk of adverse perinatal outcomes: a meta-analysis. JAMA, 295(15), 1809. https://doi.org/10.1001/jama.295.15.1809；Schummers L, Hutcheon JA, Hernandez-Diaz S, et al. (2018). Association of Short Interpregnancy Interval With Pregnancy Outcomes According to Maternal Age. JAMA Internal Medicine, 178(12), 1661. https://doi.org/10.1001/jamainternmed.2018.4696；World Health Organization (2007). Report of a WHO Technical Consultation on Birth Spacing, Geneva, 13–15 June 2005（WHO/RHR/07.1）. https://www.who.int/publications/i/item/WHO-RHR-07.1；Ball SJ, Pereira G, Jacoby P, de Klerk N, Stanley FJ (2014). Re-evaluation of link between interpregnancy interval and adverse birth outcomes: retrospective cohort study matching two intervals per mother. BMJ, 349, g4333. https://doi.org/10.1136/bmj.g4333（备注里的反方研究）