Getting pregnant while breastfeeding is safe for most healthy women, and it happens more often than many people expect. Your body can support both a growing fetus and a nursing child, though you’ll likely notice changes in your milk supply, your energy levels, and how breastfeeding feels. Whether you continue nursing through pregnancy or decide to wean is a personal choice, and understanding what to expect can help you make it confidently.
How Pregnancy Happens During Breastfeeding
Many women assume breastfeeding acts as reliable birth control, and there’s some truth to that, but only under narrow conditions. The lactational amenorrhea method (LAM) offers about 98% protection from pregnancy, but only when three criteria are met simultaneously: your period hasn’t returned, your baby is exclusively breastfed with no supplements, and your baby is under six months old. Once any of those conditions change, your fertility can return quickly.
Without strict LAM use, the pregnancy rates climb noticeably. Studies show cumulative pregnancy rates of about 2.9 per 100 women by six months and 5.9 per 100 women by 12 months of breastfeeding. As your baby starts sleeping longer stretches at night, eating solid foods, or nursing less frequently, your body begins cycling again, sometimes before you ever see a period. That means your first ovulation after birth can catch you off guard.
Is It Safe to Keep Breastfeeding?
The biggest concern most women have is whether breastfeeding could trigger a miscarriage or preterm labor. The short answer: in a healthy pregnancy, the evidence consistently says no. Although breastfeeding releases oxytocin, which causes uterine contractions, the amount released during nursing is small. More importantly, the uterus is essentially “deaf” to oxytocin throughout most of pregnancy. Research has shown that even high doses of synthetic oxytocin cannot trigger labor until a woman is at or near full term.
Multiple studies reinforce this. One found no differences in infection, hypertension, bleeding, or preterm delivery between women who breastfed during pregnancy and those who didn’t. Another found the miscarriage rate was 7.3% in breastfeeding women compared to 8.4% in non-breastfeeding women, a statistically insignificant difference. A third study actually found a lower rate of miscarriage in the breastfeeding group and concluded that breastfeeding does not increase the risk of miscarriage, preterm birth, or low birth weight.
That said, some higher-risk situations call for a conversation with your provider. If you have a history of preterm labor, cervical insufficiency, or are carrying multiples, your doctor may recommend weaning. The general guidance applies to uncomplicated pregnancies in well-nourished women.
What Changes in Your Milk
Your milk supply will almost certainly drop during pregnancy, typically around the fourth or fifth month. This is driven by rising progesterone levels, and there isn’t much you can do to prevent it. Some nursing toddlers self-wean during this time because the volume decreases and the taste changes. Others don’t seem to mind.
By late pregnancy, your body begins producing colostrum for the new baby. This is the thick, yellowish “first milk” packed with antibodies. If your older child is still nursing, they’ll be getting colostrum too. This transition is normal and won’t deprive your newborn of what they need, as your body ramps up full milk production after birth in response to the new baby’s feeding.
Your Body Needs More Fuel
Pregnancy and breastfeeding each demand significant extra energy on their own. During pregnancy, caloric needs increase by about 340 calories per day in the second trimester and roughly 450 calories per day in the third. Breastfeeding requires an additional 500 calories per day beyond what non-pregnant women need. When you’re doing both at once, those needs stack up.
Research confirms that breastfeeding during pregnancy does not pose a risk of maternal malnutrition in well-nourished women, though it may create shortages in specific nutrients. Prioritizing nutrient-dense foods, staying well-hydrated, and continuing your prenatal vitamin becomes especially important. Pay attention to hunger cues and eat when you’re hungry. This isn’t the time to restrict calories.
Nipple Pain and Nursing Aversion
One of the most common and least discussed challenges is how breastfeeding feels during pregnancy. Many women experience intense nipple sensitivity driven by pregnancy hormones, making nursing sessions uncomfortable or even painful. This is one of the most frequently cited reasons women wean during pregnancy.
Beyond physical discomfort, some women develop what’s known as breastfeeding aversion and agitation, or BAA. This involves sudden, intense negative emotions triggered specifically by nursing: anger, a skin-crawling sensation, an overwhelming urge to unlatch the child, or deep irritability while the baby is at the breast. In one survey of nearly 700 breastfeeding women, about 70% reported experiencing BAA at some point. Pregnancy is a known trigger, likely because of the hormonal shifts combined with the sheer physical demands of sustaining both lactation and a growing fetus.
These feelings can be confusing and guilt-inducing, especially for women who previously enjoyed breastfeeding. It helps to know that BAA is a recognized physiological response, not a reflection of your bond with your child. Some women manage it by shortening nursing sessions or setting limits on when they nurse. Others find it’s the signal that it’s time to wean.
Tandem Nursing After the Baby Arrives
If you continue breastfeeding through your entire pregnancy, you’ll be tandem nursing once your newborn arrives, meaning you’re feeding two children of different ages. This is entirely possible and doesn’t harm the newborn, provided the younger baby always nurses first. Prioritizing the newborn’s access ensures they get the colostrum and early milk they need.
Tandem nursing can have some surprising benefits. Research shows that milk from tandem-nursing mothers had a fat concentration about 23.5% higher and energy content about 14% higher compared to milk produced after the older child weaned. The composition of breast milk continues to evolve with the duration of lactation, adapting to the changing needs of each child.
The challenges, however, are real. In one study, 55% of tandem-nursing mothers reported tiredness, frequent night waking, and painful breasts. The exhaustion was largely driven by the newborn’s feeding frequency, which averaged about 10 to 11 sessions per 24-hour period, rather than the older child’s nursing. About 18% of mothers reported facing negative comments from family or their community, and healthcare providers were often unsupportive or unfamiliar with the practice. Only 18% of tandem-nursing mothers said they experienced no problems at all.
Deciding Whether to Continue or Wean
There’s no single right answer here. Some women nurse through pregnancy and beyond without major issues. Others find the physical discomfort, fatigue, or nursing aversion too much. Both choices are valid, and neither one is better for your older child’s long-term health or your relationship with them.
If you choose to wean, doing it gradually tends to be easier on both you and your child. Dropping one session at a time over several weeks gives your child time to adjust and helps you avoid engorgement. If your child is old enough to understand, explaining that “milk is changing” or “milk is going to sleep” can help frame the transition. Many toddlers wean themselves during pregnancy anyway, particularly when supply drops in the second trimester.
If you choose to continue, focus on nutrition, rest, and setting boundaries that make breastfeeding sustainable. Some women limit the older child to certain times of day or keep sessions short. Having a plan for tandem nursing before the new baby arrives, like always offering the breast to the newborn first, helps the transition go more smoothly.