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

Estradiol inhibits milk production. As for a possible impact on milk supply and on the breastfed child's growth curve: some treatments may reduce milk supply temporarily, but the effects seem to vary between mothers. The more a child is established on solids, the less the treatments will affect their growth curve.

The BfN factsheet (7) also raises a point that is often overlooked: if the baby is under one year old, a treatment-related drop in milk supply matters far more than for an older child, whose milk intake makes up a smaller share of their overall diet. Conversely, for a child over one year old, a reduced supply doesn't put their nutritional development at risk, even though breastfeeding still holds real value for comfort and connection.

It's also worth noting that, when planning a pregnancy, supplementing with vitamin D (10 micrograms/day) and folic acid (400 micrograms/day, or 5mg/day if a higher dose is recommended by a health professional) is compatible with breastfeeding, ideally starting 3 months before conception.

Updated Compatibility Table: Fertility Treatment Medications and Breastfeeding

This table draws on and expands the data from the Breastfeeding Network (BfN) factsheet "Fertility Treatment and Breastfeeding," published June 2025 (7). It reflects medications used in UK protocols; protocols used in other countries may differ.

Treatment phase / category	Medication (brand name)	Compatibility with breastfeeding	Points to note
GnRH agonists (down-regulation)	Decapeptyl®, Gonapeptyl® Depot, Savacyl® (triptorelin), Zoladex® (goserelin), Prostap®/Staladex® (leuprorelin), Synarel® (nafarelin)	No published data specific to breastfeeding; large protein molecules unlikely to pass into milk	May sometimes raise prolactin (unexpected increase in supply) or, conversely, lower it (drop in supply), particularly early in breastfeeding; caution advised
GnRH agonist (nasal spray)	Suprecur®, Suprefact® (buserelin)	Passage into milk very low to undetectable in available studies; no adverse effects reported in breastfed infants	Possible reduction in supply cannot be ruled out; caution advised
GnRH antagonists	Cetrotide® (cetrorelix), Ovamex®, Fyremadel® (ganirelix)	Protein molecules with low milk transfer, but a long half-life	An alternative that clears the body more quickly may be preferred because of this long half-life
Ovarian stimulation (FSH)	Gonal-F®, Ovaleap®, Bemfola®, Pergoveris® (follitropin alfa), Rekovelle® (follitropin delta), Fostimon® (urofollitropin), Menopur®, Meriofert®, Menogon® (menotrophin, FSH + LH)	Compatible; large protein molecules poorly secreted into milk and broken down in the infant's stomach	Possible reduction in supply, worth monitoring especially if the child is under one year old
Ovulation trigger (hCG)	Ovitrelle® (choriogonadotropin alfa), Zivafert® (chorionic gonadotropin)	Compatible; large molecule with low milk transfer, broken down in the infant's stomach	May instead raise prolactin and therefore milk supply
Ovulation induction (aromatase inhibitor)	Letrozole® (Femara®)	Not compatible with breastfeeding: expected to pass into milk in amounts high enough to affect the child	Clears the body in around 10 days; if breastfeeding is to continue, it is recommended to express and discard milk during treatment and for 10 further days after the last dose
Ovulation induction (SERM)	Tamoxifen®	Not compatible with breastfeeding	Reduces prolactin (risk of reduced supply even if breastfeeding is well established); can take up to 100 days to clear the body
Ovulation induction (SERM)	Clomifene®/Clomid®	Use with caution; very limited breastfeeding data	Milk levels expected to be relatively low, but can remain in the system for up to 35 days; may lower prolactin and reduce supply, a significant point if the child is under one year old
Insulin sensitiser	Metformin® (Glucophage®)	Compatible with pregnancy and breastfeeding	—
Antiplatelet	Low-dose aspirin (75-150mg/day)	Can be used with caution while breastfeeding	Theoretical risk of Reye's syndrome; if the child develops a fever, treatment or breastfeeding can be temporarily paused per professional advice. Higher, pain-relief doses of aspirin are not compatible
Corticosteroids	Hydrocortisone® (Solu-Cortef®)	Compatible	Low levels in milk, clears the body in 10-15 hours; high, prolonged doses warrant monitoring, and high doses may temporarily reduce supply
Corticosteroids	Prednisolone®	Compatible up to 40mg/day	Clears the body in 5-10 hours at these doses; above 40mg/day or with a long course, the child may need additional monitoring
DHEA	Prasterone (DHEA)	Not currently recommended given available evidence	Reduces milk supply, may lower HDL ("good" cholesterol), effect on androgens in milk unclear; no breastfeeding-specific data available
Progesterone	Cyclogest®, Lutigest®, Crinone®, Utrogestan®, Gepretix®, Lubion®	Compatible	Does not affect supply once breastfeeding is established (6-8 weeks)
Combined hormonal contraception	Combined oestrogen-progestogen pill	Compatible from 6 weeks postpartum	May reduce supply in some women, a significant point if the child is under one year old
Oestrogens	Oestrogel®, Evorel®, Estraderm®, Estradot®, FemSeven®, Lenzetto®, Progynova® TS, Sandrena®, Zumenon®, Elleste® Solo, Progynova® (tablets)	Compatible, regardless of the breastfed child's sex	May reduce supply, particularly worth monitoring if the child is under one year old
Dopamine agonists	Bromocriptine, Cabergoline	Compatible for the child if present in milk	Significantly reduce milk supply (in fact used to stop lactation); caution with uncontrolled high blood pressure (stroke has been reported postpartum)

5. Stopping Breastfeeding During Treatment: Supporting the Emotional Side

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If stopping breastfeeding becomes necessary during a fertility treatment, this decision can bring up a range of emotions for both mother and child: relief for some, sadness or grief for others, especially if it happens earlier than they would have chosen. Lactation professionals have a role to play in supporting this weaning process and listening to the mother's experience, whatever it may be.

It's also worth reminding families that if the older child wants to resume breastfeeding once the new baby arrives, tandem nursing is entirely feasible.

In Conclusion

Dallagiovanna et al. (2) state that the available evidence is insufficient to justify denying breastfeeding mothers access to fertility treatment.

Every family is unique, and the decision to wean a first child in order to restart fertility treatment should be made in partnership with health professionals, taking into account the benefits of extended breastfeeding for the older child and for the mother-child dyad — but also, as the BfN factsheet highlights, the fact that some treatments (letrozole, tamoxifen) are simply not compatible with continued breastfeeding, regardless of the child's age.

Other things worth considering include:

• how long weaning a toddler can take (who will generally have a strong opinion on the matter!)

• the exhaustion of fertility treatment while caring for a young child who needs a lot of presence and closeness. In this case, weaning can allow someone else to take over some of that care.

For further reading, you may find it helpful to consult the CRAT, e-lactancia, and the full Breastfeeding Network factsheet on fertility treatment and breastfeeding.

Bibliography

1. Elise Armoiry, Overview of Amy Brown's book: Why breastfeeding grief and trauma matters

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 created medication factsheets 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.

7. Breastfeeding Network. Fertility Treatment and Breastfeeding. Version 1.0, June 2025.

   
   

Disclaimer: This article is intended to provide general information and does not replace medical advice. It is essential to consult a healthcare professional for any question relating to your personal situation. The protocols and medications mentioned reflect UK practice in particular; protocols used in other countries (including France) may differ.