Most guidance points to 36 to 37 weeks of pregnancy as the standard time to begin expressing breast milk, specifically through a technique called antenatal colostrum harvesting. This isn’t full-scale pumping with an electric breast pump. It’s gentle hand expression of colostrum, the thick, nutrient-dense first milk your body starts producing well before your baby arrives. Starting at 36 weeks gives you time to collect and freeze small amounts while staying within a window considered safe for low-risk pregnancies.
Why 36 Weeks Is the Standard Starting Point
Across published studies on prenatal milk expression, the majority recommend beginning at either 36 or 37 weeks of pregnancy. The 36-week mark is especially common for women with gestational or pre-existing diabetes, who are more likely to benefit from having colostrum stored before birth. The largest and most well-known trial on this topic, known as the DAME trial and published in The Lancet, specifically advised women with diabetes in pregnancy to begin expressing at 36 weeks and found no increased risk of harm compared to standard care.
A smaller number of studies have explored starting earlier, between 32 and 36 weeks, but there’s no broad consensus supporting that timeline yet. If your provider suggests a different starting point based on your specific situation, that guidance takes priority over general recommendations.
The Concern About Preterm Labor
The reason this question comes up at all is oxytocin. Nipple stimulation triggers your body to release oxytocin, the same hormone hospitals use (in synthetic form) to induce labor. That connection naturally raises the question of whether expressing milk during pregnancy could cause contractions or preterm birth.
The evidence so far is reassuring. In breastfeeding women, oxytocin levels spike within about one minute of breast stimulation but return to baseline within six minutes after stopping. Researchers have noted that even during active labor, natural oxytocin spikes don’t reliably correlate with uterine contractions, suggesting the body has additional mechanisms controlling when real labor begins. A brief session of hand expression, typically around ten minutes, likely produces only a temporary, modest rise in oxytocin rather than the sustained levels needed to trigger labor.
The DAME trial provided the strongest safety data: among over 300 women who expressed milk from 36 weeks, rates of NICU admission were virtually identical to the group that didn’t express (15% vs. 14%). The study concluded there is no harm in advising women at low risk of complications to express from 36 weeks.
Who Benefits Most From Prenatal Expression
Prenatal colostrum collection was originally developed for situations where breastfeeding might not go smoothly right after birth. The people most likely to benefit include:
- Women with diabetes (type 1, type 2, or gestational), because their newborns face a higher risk of low blood sugar. Colostrum helps stabilize a newborn’s glucose more effectively than formula, which can actually spike insulin production and worsen the problem. In one study, first-time mothers with diabetes who expressed before birth were significantly more likely to exclusively breastfeed during the first 24 hours.
- Women expecting babies with known conditions that may make feeding difficult, such as a cleft lip or heart condition.
- Women who’ve had breast surgery or previous difficulty with milk supply.
- Women planning a scheduled cesarean, since the recovery environment can make early breastfeeding more challenging.
Even outside these groups, having a small colostrum stash can reduce the pressure to supplement with formula in the first hours after birth, which in turn supports longer-term breastfeeding. Research shows that avoiding early formula use is associated with higher exclusive breastfeeding rates at six months.
Hand Expression, Not Electric Pumping
When people search for “pumping during pregnancy,” they’re often picturing an electric breast pump. In practice, prenatal colostrum collection is done by hand. Colostrum comes in tiny volumes, sometimes just a few drops per session, and an electric pump isn’t designed to capture such small amounts effectively. Hand expression gives you much more control and is gentler on breast tissue that may already be tender.
Research comparing hand expression to electric pumping in the early postpartum period found that mothers taught hand expression were more likely to still be breastfeeding at two months. While that study looked at the period right after birth rather than pregnancy itself, the principle holds: for small-volume colostrum collection, hand expression is the preferred method. One commonly cited protocol recommends expressing twice daily for about ten minutes per session until you go into labor or are admitted to the hospital.
What You’ll Actually Collect
Set your expectations low, at least at first. Colostrum during pregnancy can range from nothing at all to a few drops to roughly a teaspoon per session. Every amount matters. Colostrum is extraordinarily concentrated, packed with protein, antibodies, and immune factors that formula can’t replicate. Even a single syringe of colostrum brought to the hospital can make a meaningful difference if your baby needs supplemental feeding in the first hours of life.
Don’t be discouraged if nothing comes out in your first several attempts. The amount typically increases with practice, and some women never express much prenatally but still produce plenty of colostrum after birth. Prenatal expression is not a test of your milk supply.
Collecting and Storing Colostrum
You’ll need a few simple supplies: small syringes (1 to 5 mL), sterile caps for the syringes, resealable freezer bags, and labels. Many hospitals and birth centers provide colostrum collection kits, so ask your provider or check with the labor and delivery unit before buying anything.
The basic storage process works like this: express into a clean syringe, cap it, and label it with your name and the date and time. You can use the same syringe to collect multiple times over a 24-hour period as long as you refrigerate it between sessions and keep it sterile. After 24 hours, freeze the syringe inside a sealed freezer bag. Colostrum keeps in a refrigerator set to 0 to 4 degrees Celsius for up to five days, but freezing is the safer long-term option.
When it’s time to head to the hospital, transport your frozen syringes in a cooler bag with ice packs so they don’t thaw. Once colostrum has been defrosted, it should not be refrozen. Most hospitals suggest bringing no more than about 15 syringes.
When to Hold Off
Prenatal expression is considered safe for low-risk pregnancies at 36 weeks and beyond, but certain situations call for caution. If you have a history of preterm labor, cervical insufficiency, placenta previa, or are at elevated risk for premature birth for any reason, the oxytocin released during expression is a legitimate concern even if the effect is likely small. The same applies if you’re experiencing preterm contractions or have been placed on any form of activity restriction. In these cases, your OB or midwife should be the one to greenlight or rule out prenatal expression based on your individual risk profile.
If you do start expressing and notice regular tightening or cramping that doesn’t ease after you stop, take that as a signal to pause and bring it up at your next appointment.