Most health professionals recommend waiting until 36 to 37 weeks of pregnancy before you start expressing breast milk, and hand expression is strongly preferred over an electric pump. Before that point, stimulating your breasts can trigger the release of oxytocin, the same hormone that causes labor contractions, which raises concerns about preterm labor. Here’s what you need to know about timing, technique, and who should avoid it altogether.
Why 36 Weeks Is the Standard Starting Point
Your breasts begin producing colostrum, a thick, nutrient-dense early milk, well before your baby arrives. But the reason you’re told to wait has nothing to do with milk production. It’s about your uterus. Nipple stimulation triggers your pituitary gland to release oxytocin in small pulses. That oxytocin acts on the uterus and can cause contractions. Before 37 weeks, those contractions could potentially push your body toward premature labor.
At 36 to 37 weeks, your pregnancy is considered early term, and the risk of triggering harmful preterm contractions drops significantly. NHS guidelines advise that midwives introduce the concept of colostrum harvesting around 32 to 33 weeks, with actual collection beginning no earlier than 36 weeks. You start with just a few minutes once a day.
The largest safety trial on this topic, published in The Lancet, followed 635 women with diabetes in pregnancy. Half were advised to begin expressing at 36 weeks, and the other half received standard care. NICU admission rates were virtually identical between the two groups (15% vs. 14%), and the researchers concluded there is no harm in expressing breast milk from 36 weeks for women at low risk of complications.
Hand Expression vs. Electric Pump
During pregnancy, hand expression is the recommended method. Electric breast pumps create stronger, more sustained suction that can release more oxytocin than gentle hand expression. That distinction matters when you’re trying to minimize uterine stimulation. Hand expression gives you more control over pressure and duration, and the volumes you’ll collect are tiny anyway, often less than a milliliter per session, so a pump offers no real advantage.
There’s also evidence that hand expression supports better breastfeeding outcomes overall. In a randomized trial of mothers with newborns who were feeding poorly, those assigned to hand expression were significantly more likely to still be breastfeeding at two months (97%) compared to those who used an electric pump (73%). Mothers also found hand expression instructions clearer and felt more comfortable with the technique. For these reasons, hand expression is the better choice both during pregnancy and in the early days after birth.
Who Benefits Most From Early Colostrum Harvesting
Colostrum harvesting during pregnancy is particularly valuable if you have gestational diabetes or pre-existing diabetes. Babies born to mothers with diabetes are at higher risk of low blood sugar after birth because of fetal-neonatal hyperinsulinism. Having a small stash of frozen colostrum means your baby can receive your own milk immediately rather than formula if their blood sugar needs stabilizing. Colostrum is more effective than formula at helping newborns regulate their glucose levels during that critical transition after birth.
In Australia and New Zealand, antenatal colostrum harvesting has become routine care for women with diabetes in pregnancy. Beyond diabetes, it can also be helpful if you’re expecting a baby with a known condition like cleft palate or a heart defect that may make early feeding difficult, or if you’re planning a cesarean section and want colostrum available in case your milk takes longer to come in.
How to Collect and Store Colostrum
When you start at 36 to 37 weeks, express for just a few minutes once a day. You’ll collect very small amounts, sometimes only drops. Use a sterile syringe (your midwife or hospital can provide these) to draw up the colostrum and cap it. Label each syringe with the date and freeze it. Frozen colostrum can be transported to the hospital in a cool bag when you go into labor.
Don’t be discouraged by how little comes out. Colostrum is produced in tiny quantities by design. A newborn’s stomach holds only about 5 to 7 milliliters at a time in the first day, so even a few syringes of frozen colostrum can cover several early feeds.
When You Should Not Express During Pregnancy
Some pregnancies carry risks that make any nipple stimulation unsafe. You should avoid expressing colostrum if you have a history of miscarriage or pregnancy loss, a previous premature delivery, bleeding during pregnancy, or if you’re currently experiencing signs of preterm labor such as regular contractions, pelvic pressure, or changes in vaginal discharge before 37 weeks.
If you notice contractions starting during a hand expression session, stop immediately. Occasional tightenings (Braxton Hicks) are normal in late pregnancy, but rhythmic, painful contractions that don’t ease up after you stop expressing are a signal to put the session on hold. Women carrying multiples or those with a cervical insufficiency should also avoid prenatal breast stimulation, since these pregnancies already carry a higher baseline risk of preterm labor.
What About Using a Pump to Induce Labor at Full Term
You may have heard that pumping can help start labor naturally once you’re past your due date. There is a physiological basis for this: the oxytocin released by nipple stimulation is identical at the molecular level to the synthetic version used in hospital inductions, and the pulsatile release pattern from natural stimulation actually mimics physiological labor more closely than a continuous IV drip. Some providers suggest breast stimulation as a gentle nudge toward labor at 39 or 40 weeks, but this should only be done with your provider’s knowledge, especially since more vigorous stimulation with an electric pump carries a greater risk of overly strong contractions.
If you’re considering pumping to encourage labor, the key difference is context. A few minutes of gentle hand expression to collect colostrum at 37 weeks is very different from extended sessions with a hospital-grade pump at 40 weeks trying to kickstart contractions. The first is about milk collection with minimal uterine effect. The second is intentionally trying to trigger labor, and the intensity needs to be matched to your specific situation.