Breastfeeding and IVF
After a first successful IVF pregnancy, our patients usually return to see us, hoping for another child. Many of them will have frozen embryos or want to do another full IVF cycle. Knowing the influence of age on IVF success and wanting their children close together in age, most women don't wait very long before returning. Many will still be breastfeeding. Should they stop breastfeeding before a frozen embryo transfer or another IVF cycle?
Let's review the biology of breastfeeding first. Breasts are well-designed to feed babies and doing so has lot of benefits as it reduces the risk of infectious, atopic, and immune diseases in the child. For the woman who is breastfeeding, there are also benefits that include a reduced risk of breast and ovarian cancer, and lower risk of type 2 diabetes and heart disease. So if you can, it's good to breastfeed.
In pregnancy, the placenta produces high concentrations of estrogen and progesterone while the brain produces high levels of prolactin. These hormones work together to get the breasts primed to make milk. Then once the placenta comes out after birth, estrogen and progesterone levels drop but prolactin stays high. In response to this high prolactin level (with low estrogen and progesterone), the breasts start to make milk. As the baby sucks on the breast (or a breast pump works), the brain is stimulated to make another hormone called oxytocin, which causes the milk to come out of the breast tissue so the baby can access the milk stored in the breasts. It's an elegant system.
The high prolactin, along with the nipple stimulation of breastfeeding, also inhibits the hormones that control the menstrual cycle. As a result, for the first weeks to months after giving birth, a woman will typically not ovulate or have her period, and will be infertile. Eventually though (typically at the 6-8 month mark in a breast-feeding woman), the prolactin levels drop and ovulation and periods return. The period can take a year or even more to return if you keep breastfeeding. The return of periods is generally a sign that your hormones have returned to normal, except for the hour or so after breastfeeding.
We know that these spikes in prolactin levels can be enough to impact on fertility. While no one has quantified the impact of these prolactin spikes on fertility precisely, we do worry that they can decrease the success of a subsequent treatment, such as a frozen embryo transfer or a fresh IVF cycle. The reason we worry is that there are prolactin receptors, not just in the breast, but also in the uterine lining and in the ovaries. The breastfeeding associated spikes in prolactin levels plausibly bind to the uterine and ovarian receptors and could impact embryo implantation.
We recognize that there is no strong evidence that breastfeeding decreases the success of these treatments, but because it might, we conservatively recommend women stop breastfeeding prior to treatment. Now, there is some wiggle room. It's fairly unlikely that the once or twice-a-day breastfeeding that many babies after 9-10 months of age engage in for comfort (rather than calories) has an impact. So we will typically tell patients that once or twice a day of breastfeeding can continue with presumably no negative effect.
Ideally you will wean off breastfeeding prior to IVF and frozen embryo transfer but complete cessation is likely not necessary if you are just engaging in one or two "comfort" breastfeeds per day.