Authors

Sofia Gaggiotti Marre, MD, PhD
Gynecologist and Obstetrician
Specialist physician in fertility treatments
Puigvert Foundation-Sant Pau Hospital
Fertty, Spain

Beatriz Álvaro Mercadal, MD, PhD
PhD in Gynecology and Obstetrics
Specialist physician in fertility treatments
Puigvert Foundation-Sant Pau Hospital

Introduction

Many women who are breastfeeding and must undergo fertility treatment to conceive a second child find that healthcare professionals advise or even oblige them to stop breastfeeding in order to
carry out treatment.

Just as there are professionals who still advise against laser hair removal, surgery, or tattoos during breastfeeding, it is possible that they do so as well with fertility treatments for various reasons: a lack of information, fear that the medication given may have teratogenic effects on future children or because of the belief that when breastfeeding, there will be worse results. Or because of the belief that when breastfeeding, there will be worse results because of the fear of not being able to stimulate correctly when there is amenorrhea or when prolactin levels are high, and so on.

But remember that breastfeeding is not only about nutrition but also about nourishing and accompanying a child in many more ways and is hence, a totally personal decision of each mother and family. The approach of professionals who accompany patients in fertility treatments should not be aimed at giving an opinion on the choice of whether or not to continue with breastfeeding but rather to inform about breastfeeding, the options, and the evidence that exists in this regard. We should, of course, keep in mind several factors, such as the age of the patient and the age of the breastfeeding child, frequency of breastfeeding, whether or not there is amenorrhea, diseases, or comorbidities, as well as whether there is the mother’s and the infant’s desire to wean in the near future or not.

This guide reviews the current evidence on the possibilities that exist for breastfeeding when undergoing fertility treatments.

 

Effect of breastfeeding on human reproduction

Lactational amenorrhea and ovulation

Hyperprolactinemia associated with breastfeeding induces amenorrhea that can hinder spontaneous pregnancy due to no ovulation. However, amenorrhea varies greatly from person to person, ranging from a few months to more than two years or for the entire duration of lactation (Diaz 1990).

It is impossible to estimate when spontaneous ovulation will resume, so breastfeeding should not be considered an effective method of birth control (Van der Wijden C. 2015). Even so, the lactational amenorrhea method (LAM) stipulates that if certain requirements are met, the chances of spontaneous ovulation (and, therefore, a pregnancy) are practically zero (GenCat, MELA 2021).

Pregnancy during lactation

If ovulation reappears, there is a chance of conceiving, which is why there are pregnant women who are breastfeeding and have not menstruated. Thus, it is not necessary to stop breastfeeding when a new pregnancy is desired.

It should be taken into account that the most determining factor in achieving an evolutionary pregnancy is the woman’s age. The older a woman is, the more difficult it is to achieve a pregnancy, mainly in relation to a worsening of the oocyte quality associated with an increase of aneuploidies (chromosomal alterations) in the generated embryos. There are many beliefs about the possible negative effect of breastfeeding on the new pregnancy. However, many women all over the world are pregnant and breastfeeding simultaneously or even choose tandem breastfeeding two children after the birth of the next baby.

Risk of miscarriage or preterm birth: Of the studies that have compared the risk of miscarriage or preterm birth between breastfeeding and non-breastfeeding women, none of them have found significant differences. Therefore, there is no evidence that breastfeeding can cause miscarriage or preterm delivery in an ongoing pregnancy (López-Fernández et al; 2017).

Quantity and composition of milk: Studies show that only 12-34% of women who conceive while breastfeeding continue breastfeeding throughout pregnancy. Most of the time, the decision to wean is the mother’s decision. However, a decrease in milk production during pregnancy has been demonstrated due to the high concentration of estrogen and progesterone during pregnancy. It has been reported that in up to 18% of the cases, milk production may cease completely (López-Fernández et al; 2017).

In turn, the composition of breast milk is slightly different between breastfeeding and non-breastfeeding pregnant women, although the clinical relevance of this finding, if any, is unclear (López-Fernández et al; 2017).

Fertility treatments during the period of lactation

Delayed motherhood, gynecological pathologies (tubal factors, endometriosis, etc.), andrological pathologies (quality of semen, alterations in ejaculation, etc.), or mixed, or the desired family planning situation (single women or women with a female partner, co-parenting constellations, etc.) lead many individuals and couples to require fertility treatments in order to fulfill their desire to have children.

There are several scenarios in which a breastfeeding person may consider undergoing assisted fertility treatment, among them:

• Having had a first baby through fertility treatment by artificial insemination or in vitro fertilization (IVF) and not having frozen embryos, a new treatment is needed in order to expand the family.
• Availability of frozen embryos from a previous cycle.
• A person who was not pregnant and has induced lactation and wishes to undergo fertility treatment in order to conceive or to be able to generate embryos of their own body.
• Diagnosis of a disease or entity that requires gonadotoxic treatment or ovarian surgery and egg retrieval and vitrification is desired.

In these situations, there are several treatment options:

• Ovarian stimulation for IVF or artificial insemination
• Endometrial preparation for frozen embryo transfer
• Induction of ovulation

No data is available on the difference in the outcomes of lactating versus non-lactating women during fertility treatment.
As for the possible teratogenic effect of the medications used, it should be noted that most of them are hormones that are naturally present in the woman’s body and that their passing into breast milk has been scarcely studied.

We will analyze in detail the characteristics of each of the treatments.

Ovarian stimulation for oocyte vitrification, In Vitro Fertilization (IVF), or artificial insemination and lactation

IVF treatment requires ovarian stimulation with high doses of gonadotropins for 10 – 12 days, followed by the administration of recombinant hCG or analogs of the gonadotropin-releasing hormone (GnRH) to induce ovulation. Subsequently, the oocytes are extracted by follicular puncture under sedation.

In the case of artificial insemination, the treatment is the same, but with lower doses and without the need for surgical intervention.

Gonadotropins: There has been no evidence of a deleterious effect of using gonadotropins during breastfeeding.

There are human follitropin preparations (urofollitropin from human menopausal gonadotropin (HMG)) or placental and others obtained by recombinant engineering (follitropins alpha, beta and delta and corifolitropin alpha) with similar uses and effectiveness (Weiss, 2019).

Although there are no published studies on their excretion in breast milk, their high molecular weight makes this very unlikely (Breitzka RL, 1997). They are glycoproteins with practically no oral bioavailability, so they are inactivated in the gastrointestinal tract. This means that if it were to be ingested through breast milk by the infant, it would not be absorbed or passed into the infant’s plasma. In premature infants and in the immediate neonatal period, there may be greater intestinal permeability, so the risk of absorption may be slightly increased (Breitzka RL, 1997).

In spite of this, some technical data sheets of these drugs state that they are not recommended in breastfeeding women, due to the lack of studies in this regard.
The estrogenic effect resulting from ovarian stimulation with gonadotropins has not been shown to decrease milk production.

Follicular puncture under anesthesia: The possible anesthetics used to perform follicular puncture are compatible with breastfeeding (Mitchell, 2020).

Embryo transfer and lactation

Once the embryos have been obtained, they can be transferred in the same IVF cycle (fresh transfer) or in a delayed cycle after vitrification (cryotransfer).

Fresh transfer

Fresh transfer requires the administration of micronized natural progesterone vaginally from the day of egg retrieval until the first weeks of pregnancy. Progesterone does not affect milk production, is excreted in non-significant amounts, and no alterations have been observed in the infants of mothers who took it (National Institute of Child Health and Human Development, 2006).

Cryotransfer

Regarding endometrial preparation for vitrified embryo transfer, endometrial preparation can be performed by natural cycle (detecting ovulation by ultrasound and hormonal determination), modified natural cycle (administering recombinant hCG after observation of the dominant follicle), artificial cycle (by administering estrogens during the follicular phase and progesterone from embryo day 0) or ovulation induction in cases of amenorrhea.

Estrogens and progesterone are both safe medications during lactation and can be administered (Pinheiro 2016, Croxatto 1987). However, if the patient presents regular cycles, it is recommended to opt for a natural or modified natural cycle for its benefits in terms of endogenous hormonal secretion of the cycle.

In the case of amenorrhea, either due to lactation or to the patient’s underlying pathology (polycystic ovary, central amenorrhea, etc.), a stimulated cycle can be chosen, administering low doses of gonadotropins until follicular recruitment is evident. In the case of lactational amenorrhea and ovulation induction, it should be taken into account that achieving ovulation may be longer than usual or very difficult, which may lead to cancellation of the cycle (own data, unpublished).

Induced ovulation and breastfeeding

When inducing ovulation in a lactating woman, either for artificial insemination, programmed intercourse, or to program an embryo cryotransfer, it is possible to use gonadotropins and hCG for ovulation induction (as discussed in the IVF section) or Clomiphene Citrate or Letrozole.

As for Clomiphene Citrate, the evidence is scarce, but its use can be authorized if lactation is well established and if it is used in the recommended doses and for short periods of time.
On the contrary, Letrozole could be excreted in breast milk in significant quantities and also have an effect on breastfeeding. It is advisable to stop breastfeeding before using Letrozole and to wait about 10 days before resuming breastfeeding, so it is difficult to make the use of this drug compatible with a continuation of breastfeeding.

Other considerations

In case of a new pregnancy with an infant younger than 6 months who has not started complementary feeding and introducing solids, the adequate growth of the infant should be monitored (AEP, 2015).
Therefore, in order to reassure families about the correct nutritional intake of the infant and in order to avoid a very short inter-gestational period, a minimum age of 6 months for the infant would be recommended before submitting the breastfeeding woman to fertility treatment.