Nursing multiples: how your milk is affected by nursing more than one child

Image courtesy of Doula Barcelona

When a mother finds out she’s carrying twins, or discovers she’s pregnant while still nursing her toddler, the question that arrives almost immediately is the same one: will there be enough for my baby? Over 35 years ago, my mother was categorically told, "No," and not to even try to nurse my younger sisters.

It’s a reasonable fear and it’s one that gets very little honest answering, partly because the research on feeding more than one child is genuinely thin and partly because we’ve inherited a cultural idea of milk as a finite resource that gets divided up and rationed out, as though your body were a jug (no pun intended) with a line drawn on it.

It isn’t. Your breasts are not jugs and they never were. Your body is a living, listening organism that has spent the whole of human history working out how to feed whoever turns up - and it’s far cleverer than anyone has bothered to tell you.

Your supply isn’t fixed

The single most important thing to understand is that milk production is regulated locally, in each breast, by how much milk is removed from it.

There’s a protein in your milk called the feedback inhibitor of lactation, and it does exactly what the name suggests. When milk sits in the breast, that inhibitor accumulates and tells the milk-making cells to slow down. When milk is removed, the inhibitor goes with it and production speeds back up (1,2). This is why the two breasts of the same woman can produce wildly different volumes on the same day. It’s also why the outdated advice to, "Wait until you fill up," does the precise opposite of what mothers hope. Your body isn’t dividing a set quantity of milk between however many children are asking for it. It’s responding, breast by breast and feed by feed, to whoever is asking. More demand builds more supply. That’s not a platitude, it’s the mechanism.

This means that each breast is holding its own quiet conversation with the child at it. Two children, two conversations, running at the same time in the same body.

What the twin and triplet data actually shows

This is where it gets remarkable. In foundational Australian work on this, eight mothers exclusively or partially breastfeeding twins were studied by test weighing, alongside one mother feeding triplets. At six months, individual breasts of the fully breastfeeding mothers were yielding between 0.84 and 2.16 kg per twenty-four hours, and the mothers were feeding an average of 15.4 times a day. The mother of triplets, whose babies were two and a half months old, was producing 3.08 kg of milk in twenty-four hours across twenty-seven feeds (3).

Three litres a day. From one woman, twenty-seven times over, around the clock, out of her own body.

Crucially, the composition held up. Lactose, protein and fat concentrations varied between mothers, as they always do, but they sat within adequate ranges across every group (3). The milk wasn’t 'thinned out,' or diluted to cover the extra children. This isn’t a fluke of one small study, either. When 125 mothers of very preterm babies were compared, those with multiples produced significantly more milk over twenty-four hours than those with singletons, 599 mL against 430 mL, despite similar pumping frequency and otherwise comparable circumstances (4). Something about carrying and birthing more than one baby appears to prime the breast for greater output before a single feed has happened.

Tandem nursing: the colostrum question

If you’re pregnant and still nursing an older child, the worry usually isn’t volume, it’s colostrum. Mothers ask me constantly whether their toddler will drink the newborn’s first milk before the baby ever gets to it. They won’t. From around the sixteenth to twentieth week of pregnancy, your milk quietly begins converting back towards colostrum, driven by pregnancy hormones rather than by demand, which is also why your supply often drops in pregnancy no matter how frequently your older child nurses. That colostrum will be there after the birth regardless of how much the toddler has fed (5).

Your body starts preparing for your new baby months before you meet them, while you’re still feeding the last one. It doesn’t stop to ask you whether you can manage both. It simply assumes you can and gets on with making what each of them needs.

What the composition research shows is reassuring too. When milk from tandem-breastfeeding mothers was compared with milk from mothers feeding one child, colostrum and mature milk were broadly similar between the two groups, with carbohydrate content the only meaningful difference (6).

A more recent case-control study found no significant differences in macronutrient composition between tandem and singular breastfeeding at either the colostrum or mature milk stage (7). Work looking beyond macronutrients, at the metabolite and microbial fingerprint of the milk, similarly found no difference between tandem-feeding and single-nursling pairs (8).

There’s one finding I particularly love: in a Polish cohort of thirteen tandem-feeding mothers, milk had higher fat, higher total protein and higher energy value during tandem feeding than the same mothers’ milk after the older child had weaned - and the composition then shifted to suit only the younger child’s needs (9). Your milk was holds both of them and the moment one of them steps away from the breast, it recalibrates around the one who remains, without you doing a single thing differently. That is not a small thing. That is your body keeping track of two separate children, in the dark, while you sleep.

Boys, girls and what we honestly don’t know

You’ll have seen the claim that mothers make different milk for sons and daughters, which matters if you’re carrying one of each. In other mammals, this is well established: rhesus macaques produce richer milk for sons and more of it for daughters and dairy cattle yield more for female calves (10). In humans, the picture is genuinely messy. Powe and colleagues found more energy-dense milk for male infants among well-nourished American mothers (11). A Kenyan study found richer milk for sons among better-off mothers but richer milk for daughters among poorer ones (12). Other researchers have found no sex bias at all (13) and the major review of this literature concluded the evidence is limited and contradictory (14), but boys do appear to drink around 5% more (15).

So if you’re nursing a boy and a girl, I’d stop short of telling you your body is making bespoke milk for each. We don’t know that for sure. What we do know is that both will get milk that’s adequate, and that assigning a breast to each child, which many mothers of twins do anyway for practical reasons, means each breast will calibrate to that child’s appetite through the local feedback mechanism.

The real limiting factor

Notice what none of this evidence points to. Insufficient milk remains the most commonly cited reason mothers of multiples stop breastfeeding, but there’s no evidence it’s more common in twins than in singletons, which tells you it’s a perceived problem rather than a physiological one (16). Your body can almost certainly do this - just as my mother's likely could. Whether you can do it depends on something else entirely: whether anyone shows up to hold the other baby, bring you food and drinks and let you lie-in after a night of alternating feeding two or more babies?

If you’re carrying twins, or growing one baby while another is still at your breast and you’re lying awake wondering whether there’ll be enough of you to go round, I want you to hear this: There is enough milk. Your body worked that out a very long time ago and it has never once needed your permission. The bigger question is, do you have enough support? The answer to that has never been any mother's body failing. It's all of ours.

With love,

Danielle

❤️

References:

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2. Daly SE, Owens RA, Hartmann PE. The short-term synthesis and infant-regulated removal of milk in lactating women. Exp Physiol. 1993;78(2):209–20.

3. Saint L, Maggiore P, Hartmann PE. Yield and nutrient content of milk in eight women breast-feeding twins and one woman breast-feeding triplets. Br J Nutr. 1986;56(1):49–58.

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7. Macronutrient composition of breast milk in tandem and singular breastfeeding: a case–control study. Adv Neonatal Care. 2025. doi:10.1097/ANC.0000000000001318

8. Human milk from tandem feeding dyads does not differ in metabolite and metataxonomic features when compared to single nursling dyads under six months of age. Metabolites. 2022;12(11):1069.

9. Sinkiewicz-Darol E, et al. Tandem breastfeeding: a descriptive analysis of the nutritional value of milk when feeding a younger and older child. Nutrients. 2021;13(1):277.

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11. Powe CE, Knott CD, Conklin-Brittain N. Infant sex predicts breast milk energy content. Am J Hum Biol. 2010;22(1):50–4.

12. Fujita M, Roth E, Lo YJ, Hurst C, Vollner J, Kendell A. In poor families, mothers' milk is richer for daughters than sons: a test of Trivers–Willard hypothesis in agropastoral settlements in Northern Kenya. Am J Phys Anthropol. 2012;149(1):52–9.

13. Quinn EA. No evidence for sex biases in milk macronutrients, energy, or breastfeeding frequency in a sample of Filipino mothers. Am J Phys Anthropol. 2013;152(2):209–16.

14. Galante L, Milan AM, Reynolds CM, Cameron-Smith D, Vickers MH, Pundir S. Sex-specific human milk composition: the role of infant sex in determining early life nutrition. Nutrients. 2018;10(9):1194.

15. da Costa TH, Haisma H, Wells JC, Mander AP, Whitehead RG, Bluck LJ. How much human milk do infants consume? Data from 12 countries using a standardized stable isotope methodology. J Nutr. 2010;140(12):2227–32.

16. Multiple Births Foundation. Guidance for health professionals on feeding twins, triplets and higher order multiples. London: Multiple Births Foundation; 2011.