Breastfeeding and ART: Impact of Lactation on Fertility Treatments

Although breastfeeding provides contraception in the first months postpartum, some mothers become pregnant while breastfeeding, and some even choose to tandem-nurse their second child. Breastfeeding during pregnancy is relatively common, particularly in low-income countries where contraceptive methods are less readily available.

The desire to expand one’s family while continuing to breastfeed is a legitimate wish for many women undergoing assisted reproductive technology (ART). However, this raises many questions. This article explores the interactions between breastfeeding and fertility treatments.

Breastfeeding and ART.

Nursing After ART, IVF: Reclaiming the Body

Many mothers who conceived through medically assisted reproduction choose to breastfeed their child. For some, this desire is particularly strong: where their body failed to conceive, it must succeed in nourishing the child, as reflected by many mothers in a study on breastfeeding difficulties by Amy Brown (1).

For breastfeeding women who wish to have another child, ART will quickly become necessary again, perhaps even before the baby is weaned.

A literature review on this topic (2) indicates that there appear to be no epidemiological data on the number of women undergoing ART while breastfeeding, but that it is not a rare phenomenon. Mothers who have undergone ART are aware of the time it takes to achieve pregnancy and generally do not wish to wait; they are also typically deeply committed to their parenting role.

In many cases, mothers report that ART teams required them to wean their child.

So, is weaning truly mandatory?

Reasons to Consider Weaning

Healthcare professionals often advise mothers that weaning is mandatory:

• to maximise the chances of treatment success;

• to avoid potential adverse effects of treatments on the breastfed child;

• to avoid a possible impact on lactation (and therefore on the child’s growth if the child has not yet started solids).

Yet weaning is not self-evident, either for the mother or the child. Beyond nutrition, breastfeeding has proven immunological benefits in the first years of life, as well as emotional benefits: it is a mode of parenting and attachment.

1. Breastfeeding may impact fertility.

   
   

As described in this article, breastfeeding has a contraceptive effect. The rise in prolactin induced by suckling prevents ovulation, causes amenorrhoea, and produces a contraceptive effect whose duration varies depending on the woman and her nutritional status, as well as the number of feeds.

Many breastfeeding women do not experience a return of their menstrual cycle as long as a certain number of feeds is maintained, and night feeds in particular appear to be very important. The number of feeds required for fertility to return varies between individuals. If the breastfeeding mother has not had a return of her cycle, a reduction in the number of feeds may be considered.

After complete weaning, ovulation generally returns within 14 to 30 days (2).

2. Impact of breastfeeding on treatment outcomes

Regarding the possible risk of treatment failure due to breastfeeding: there are no studies on this subject (2, 3). Many testimonials from women who breastfed their child while undergoing successful fertility treatments can be found (4).

The Australian Breastfeeding Association (5) states: “If you have resumed ovulation and regular periods while continuing to breastfeed, weaning in order to begin IVF may not increase your chances of becoming pregnant.”

Furthermore, many women around the world become pregnant each year while breastfeeding.

The article by Dallagiovanna et al. (2) considers the theoretical mechanisms by which breastfeeding could negatively impact an ART pathway and raises the following points:

• Concerns regarding optimal embryo implantation and development: Physiological prolactin levels promote fertility by supporting embryo development, implantation, and through immunomodulatory and steroidogenic effects. However, excessively high prolactin levels are known to cause infertility, due to hypogonadism as well as impairment of endometrial function and interference with embryo implantation. During breastfeeding, the levels of LH required to trigger ovulation are also higher.

• A possible reduction in the efficacy of ovarian stimulation during breastfeeding is also considered.

• Uncertainty regarding the efficacy of frozen embryo transfer on a natural cycle during breastfeeding is highlighted.

• Finally, the effect of oxytocin released during suckling is highlighted, with a risk of increased uterine contractility (even though the number of oxytocin receptors in the uterus is lower than in the mammary gland and decreases markedly postpartum), potentially limiting embryo transfer.

The authors state: “Overall, the available experimental evidence is not reassuring and tends to suggest some adverse effects of breastfeeding and elevated peripheral prolactin on the hypothalamic-pituitary axis and ovarian physiology.”

However, an article published in 2025 (6) addressed this issue. This study aimed to evaluate the effect of breastfeeding on outcomes of in vitro fertilisation (IVF) and frozen embryo transfer (FET). A retrospective cohort study was conducted at a single urban fertility centre in Canada, among women who had undergone FET (2015–2023). Breastfeeding women (study group) were compared to non-breastfeeding women, matched 1:1 by age, treatment protocol, and year. Breastfeeding did not appear to be a factor influencing pregnancy rates, unlike maternal age.

3. Possible risk of treatments to the breastfed child

There is a tendency to avoid hormonal treatments in breastfeeding mothers for fear that hormones may pass into breast milk and affect the child. Transfer into milk has been demonstrated for the contraceptive pill.

In practice, many medications used during ovarian stimulation treatments are compatible with breastfeeding, with a risk considered low for the breastfed child .

4. Impact of treatments on the growth of the breastfed child

Oestradiol inhibits milk production. Regarding the possible impact on lactation and on the weight curve of the breastfed child: some treatments may transiently reduce lactation, but the effects appear to be variable between mothers. The more diversified the child’s diet and the more solids they consume, the less the treatments will impact their weight curve.

In Conclusion

Dallagiovanna et al. (2) state: The available evidence is insufficient to deny ART access to breastfeeding mothers.

Each family is unique, and the decision to wean a first child to resume an ART pathway should be made in consultation with healthcare professionals, but should also take into account the benefits of extended breastfeeding for the first child and for the mother-child dyad. The following factors should also be considered:

• How long weaning an older child may take (who will generally voice their own strong objection to the idea!);

• The fatigue associated with fertility treatments while caring for a young child who requires considerable presence and closeness. In this case, weaning may allow for a change of roles.

  
  

Bibliography

1. Elise Armoiry, Presentation of Amy Brown’s book, IPA website

2. Dallagiovanna C, Di Stefano G, Reschini M, Invernici D, Comana S, Somigliana E. Re-embarking in ART while still breastfeeding: an unresolved question. Arch Gynecol Obstet. 2025 Feb;311(2):555-565. doi: 10.1007/s00404-025-07933-8. Epub 2025 Jan 20. PMID: 39828777; PMCID: PMC11890365.

3. Lactapp Blog

4. Group of British mothers who compiled drug information sheets with Dr Wendy Jones, pharmacist.

5. Australian Breastfeeding Association.

6. Hochberg A, Kugelman N, Amikam U, Bleau V, Shochat T, Suarthana E, Buckett W. The effect of breastfeeding on treatment outcomes in in-vitro fertilization frozen embryo transfer cycles. J Assist Reprod Genet. 2025 Aug;42(8):2747-2754. doi: 10.1007/s10815-025-03556-9. Epub 2025 Jun 20. PMID: 40540121; PMCID: PMC12422992.