Hypertensive disorders affect up to 10% of pregnancies and remain a leading cause of maternal and perinatal morbidity and mortality (Cordero et al., 2021; Sun et al., 2024). As lactation professionals, we must understand the implications of perinatal hypertension—particularly preeclampsia—on lactation outcomes and how treatments like magnesium sulfate (MgSO₄) may impact early breastfeeding.

Understanding Perinatal Hypertension

Perinatal hypertension encompasses a spectrum including chronic hypertension, gestational hypertension, preeclampsia, and eclampsia. Preeclampsia specifically is marked by hypertension (≥140/90 mmHg) with proteinuria and/or evidence of end-organ dysfunction occurring after 20 weeks gestation (Demirci et al., 2018).

Preeclampsia is classified as early-onset (<34 weeks) or late-onset (≥34 weeks), with or without severe features. Severe features include thrombocytopenia, liver dysfunction, renal insufficiency, pulmonary edema, and visual or neurological disturbances (Sun et al., 2024).

Risk Factors

Common risk factors for preeclampsia include:

• Nulliparity
• Obesity
• Diabetes (Type 1 or 2)
• Advanced maternal age
• Chronic hypertension

These risks not only predispose individuals to preeclampsia but may also influence lactation success (Demirci et al., 2018).

Management and Breastfeeding

Antihypertensives and Lactation Safety

First-line medications like labetalol, nifedipine, and methyldopa are generally considered safe during lactation (Anderson, 2018). ACE inhibitors such as enalapril and captopril are minimally excreted in breastmilk and are acceptable for breastfeeding parents (Anderson, 2018). However, diuretics in high doses may reduce milk supply, although standard doses typically do not impair lactogenesis (Anderson, 2018).

Magnesium Sulfate and Breastfeeding

MgSO₄ is a critical seizure prophylaxis tool for severe preeclampsia. Traditionally, it’s administered for 24 hours postpartum, but evidence suggests that a 6-hour duration may be equally effective with fewer barriers to early breastfeeding and ambulation (Vigil-De Gracia et al., 2017).

Despite its utility, MgSO₄ can cause maternal drowsiness, nausea, and muscle weakness—side effects that may limit early breastfeeding or milk expression (Demirci et al., 2018; Cordero et al., 2021). Additionally, prolonged postpartum monitoring during MgSO₄ therapy often results in mother-infant separation, especially in hospitals where NICU admission is common for infants born to preeclamptic mothers (Samuels et al., 2012).

Breastfeeding Outcomes in Preeclampsia

Breastfeeding initiation rates among women with preeclampsia can be similar to those without it, but the mode often differs. For example, exclusive breastfeeding may depend more on expressed breast milk rather than direct feeding due to postpartum complications (Cordero et al., 2021).

Key findings include:

Maternal-infant separation during MgSO₄ therapy may delay initiation of direct breastfeeding (Demirci et al., 2018; Samuels et al., 2012).

Delayed lactogenesis II is common, particularly in women who experienced cesarean delivery, preterm birth, or prolonged MgSO₄ exposure (Demirci et al., 2018).

Intention to breastfeed remains the strongest predictor of success, even among women with severe preeclampsia (Samuels et al., 2012).

Interventions such as antenatal milk expression (AME) may help mitigate delays in lactogenesis and reduce formula supplementation in the hospital (Demirci et al., 2018).

The Role of Antenatal Milk Expression (AME)

AME may be especially beneficial for patients at risk of hypertensive disorders. In Demirci et al.’s (2018) case series, participants who practiced AME had a backup milk supply during periods of maternal-infant separation, boosting confidence and reducing reliance on formula during the early postpartum period.

Nursing Care and Guidelines

According to a 2024 systematic review of nursing guidelines, postpartum nursing care for preeclampsia should include:

• Blood pressure monitoring
• MgSO₄ safety monitoring
• Breastfeeding support and early lactation counseling
• Long-term cardiovascular risk education (Sun et al., 2024)

This aligns with strong recommendations in evidence-based guidelines to support breastfeeding as a strategy for improving long-term maternal cardiovascular outcomes.

Hypertension and Milk Supply

There is some evidence that hypertensive disorders—especially preeclampsia—are associated with delayed onset of lactogenesis II and reduced milk supply, although the mechanisms are not fully understood.

• Delayed Lactogenesis II (DLII) is more common among individuals with preeclampsia. Demirci et al. (2018) reported that several women with late-onset preeclampsia experienced DLII (milk coming in after 72 hours), even when motivated and supported. Factors may include stress, inflammation, placental dysfunction, and increased risk of cesarean delivery—all of which may affect milk production.

• Samuels et al. (2012) found that only 51% of women with severe preeclampsia initiated breastfeeding successfully, and a major contributor was maternal-infant separation and NICU admission, rather than a biologic inability to produce milk.

Other potential contributing factors include reduced prolactin response, stress hormone elevation (e.g., cortisol), and vascular changes that may impair mammary gland perfusion.

Magnesium Sulfate and Milk Supply

There is no strong evidence that magnesium sulfate directly suppresses milk production. However, indirect effects are well documented:

• Sedation, nausea, and altered mental status can reduce the frequency of early breastfeeding or expression—critical for establishing supply (Cordero et al., 2021; Samuels et al., 2012).

In one clinical trial, women who received magnesium sulfate for only 6 hours postpartum had significantly earlier breastfeeding initiation compared to those who received it for 24 hours (Vigil-De Gracia et al., 2017). Although the study didn’t measure milk volume or hormone levels, the findings suggest that reducing exposure to MgSO₄ may facilitate earlier at-breast feeds and milk expression—both crucial for supply.

Why This Matters for Lactation Professionals

1. Be proactive: Identify patients with hypertensive disorders early and collaborate on a plan to protect lactation.

1. Support expression: Encourage early and frequent milk expression when direct breastfeeding isn’t possible.

1. Know your meds: Be aware of medication safety profiles during lactation.

1. Advocate for proximity: Push for policies that minimize maternal-infant separation, even in intensive care settings.

Educate: Reinforce that breastfeeding may reduce long-term cardiovascular disease risk—a meaningful motivator for some clients (Park & Choi, 2018).

Summary for Lactation Professionals

Hypertensive disorders (especially preeclampsia) are linked with delayed lactogenesis and potentially lower milk supply, but often due to complex, multifactorial reasons (e.g., maternal stress, cesarean birth, inflammation, early separation).

Magnesium sulfate likely impacts lactation indirectly—through maternal sedation and delayed breastfeeding initiation—rather than through any direct physiological suppression of milk production.

Early lactation support, hand expression, and skin-to-skin when possible are key interventions for these patients.

References

Anderson, P. O. (2018). Treating hypertension during breastfeeding. Breastfeeding Medicine, 13(2), 95–96.

Cordero, L., et al. (2021). Breastfeeding initiation among women with preeclampsia with and without severe features. Journal of Neonatal-Perinatal Medicine, 14(4), 419–426.

Demirci, J. R., et al. (2018). Delayed lactogenesis II and potential utility of antenatal milk expression in women developing late-onset preeclampsia: A case series. BMC Pregnancy and Childbirth, 18, 68.

Goulding, A. N., et al. (2023). Breastfeeding among people with mild chronic hypertension: A secondary analysis of the CHAP trial. Am J Obstet Gynecol MFM, 5(9), 101086.

Park, S., & Choi, N. K. (2018). Breastfeeding and maternal hypertension. American Journal of Hypertension, 31(5), 615–622.

Samuels, P., et al. (2012). Breastfeeding in women with severe preeclampsia. Breastfeeding Medicine, 7(6), 457–464.

Sun, R., et al. (2024). A review of clinical practice guidelines on the management of preeclampsia and nursing inspiration. International Journal of Nursing Sciences, 11, 528–535.

Vigil-De Gracia, P., et al. (2017). Magnesium sulfate for 6 vs 24 hours post delivery in patients who received magnesium sulfate for less than 8 hours before birth: A randomized clinical trial. BMC Pregnancy and Childbirth, 17, 241.