Morphine

Pregnancy

The live MotherToBaby sheet reports one first-trimester study of 70 morphine exposures, but the primary report supporting that number was not identified. The count and finding are not repeated here as verified evidence. Broussard et al. (2011) analyzed the US National Birth Defects Prevention Study, a case-control study of 17,449 case mothers and 6,701 controls. Therapeutic opioid use was reported by 2.6% of case mothers and 2.0% of control mothers; opioid treatment was associated with several specific defects, but the study did not estimate a morphine-specific effect. Varney et al. (2024) reviewed 12 first-trimester opioid-analgesic studies; 11 were at high risk of bias. The pooled estimate for overall major malformations was not statistically clear (RR 1.04, 95% CI 0.98-1.11), and the result was for opioid analgesics as a class. Brogly et al. (2021) studied 627,172 pregnancies among 509,522 women in Ontario without opioid use disorder. Four percent of pairs were exposed to opioid analgesics, including morphine, but the study reported class-level risks and no morphine-specific estimate; preterm-birth risk was higher after first- and second-trimester opioid exposure, including morphine exposure, and after third-trimester morphine exposure. Wang et al. (2023) studied 220,570 Wisconsin Medicaid births; among 31,456 opioid-analgesic-exposed newborns, NOWS odds were higher after 30 or more exposure days and with third-trimester exposure, but not after 1-6 days. ElHassan et al. (2026) linked Arkansas records for 27,441 pregnancies; opioid purchases were associated with higher odds of preterm birth and NOWS, and higher morphine-milligram-equivalent dose was associated with higher NOWS odds. This is a class-level dose measure, not a morphine-only exposure estimate. The MS CONTIN label reports animal developmental findings and says human data do not establish a drug-associated risk for major birth defects.

Breastfeeding

Feilberg et al. (1989) measured morphine in milk from five lactating women after epidural or parenteral doses; the authors described the transferred amount as small. Baka et al. (2002) measured milk and plasma concentrations in seven mothers receiving intravenous patient-controlled morphine after cesarean delivery; morphine and its active metabolite were found in milk samples from three mothers, and the authors described likely transfer to the newborn as negligible under those study conditions. Wittels et al. (1990) compared five mothers given morphine with five given meperidine after cesarean delivery; morphine-group newborns scored higher on alertness and orientation, and respiratory rates did not differ. These small pharmacokinetic and preliminary outcome studies do not establish how often sedation, breathing problems, or other serious effects occur. LactMed reports that epidural exposure results in trivial milk amounts, while IV or oral maternal doses soon after birth produce higher milk levels; it also notes newborn sensitivity and advises monitoring. The extended-release MS CONTIN label states that lactation studies have not been conducted with extended-release morphine and advises against breastfeeding during treatment because of potential serious infant reactions.

What was tested

Human pregnancy evidence includes case-control and observational cohort studies and a systematic review of opioid analgesics as a class. MotherToBaby reports 70 first-trimester morphine exposures, and the label reports 448 exposures at any time, but the primary report behind those counts was not located; they remain unverified. The reviewed primary abstracts do not provide a morphine-specific estimate for major birth defects, preterm birth, or NOWS. Breastfeeding evidence includes small milk-concentration studies and a preliminary neonatal comparison, not large studies capable of estimating rare infant harms.