First-time moms who are older than 30, overweight or have breastfeeding difficulties on their newborn's first day may have increased odds of a delay in their full breast-milk production, a new study suggests.

After giving birth, women produce a precursor to breast milk called colostrum until their full breast milk comes in; if that shift does not happen within 72 hours, researchers consider it "delayed lactogenesis."

The concern with this is that some infants may start to become dehydrated and lose excess weight (some weight loss after birth is normal), and that some mothers, worried and frustrated, may give up on breastfeeding.

However, new moms with a delay in full milk production should not be discouraged, said Dr. Laurie A. Nommsen-Rivers of Cincinnati Children's Hospital Medical Center in Ohio, the lead researcher on the new study.

Instead, she said, they should call their pediatrician or "lactation consultant" — a specialist in breastfeeding issues who works in some hospitals and also in private practice.

With some support, Nommsen-Rivers said, mothers with delayed breast-milk production will "do just fine." She noted that nearly all new moms — 98 percent — have their milk come in within a week.

For the current study, published in the American Journal of Clinical Nutrition, Nommsen-Rivers and her colleagues looked at the factors associated with delayed lactation among 431 first-time mothers who gave birth at one California medical center.

The researchers focused on first-time mothers because they are significantly more likely than women who've given birth before to have a delay in their breast milk coming in.

Overall, the study found, 44 percent of the women took longer than 72 hours to have their milk come in — which was assessed by asking the study participants whether their breasts felt "noticeably fuller" three days after giving birth.

Women who were overweight or obese were more likely than thinner women to have a delay; 45 percent and 54 percent, respectively, compared with 31 percent of normal-weight women.

Age also appeared to be a factor, as 58 percent of women age 30 and older had a delay in their breast milk coming in, versus 39 percent of younger women.

In addition, mothers who said they had "breastfed well" at least twice during the first 24 hours of their newborn's life — when colostrum is produced — were less likely to have a delay in their milk coming in: 39 percent to 43 percent of these women had a delay, compared with 65 percent of mothers who reported only one or no instance of breastfeeding "well" in the first 24 hours.

Another factor related to delayed milk production was nipple soreness. Women who had more than mild soreness in the first few days after giving birth were less likely to have a delay than other women.

That soreness, the researchers note, may be an indicator of more-effective early breastfeeding, which would encourage full milk production.

It is not clear why relatively older age and heavier weight in the mother would be associated with a higher risk of delayed lactation, according to Nommsen-Rivers.

But both, she and her colleagues note, are related to greater odds of carbohydrate "intolerance" during pregnancy. Problems in sugar metabolism could be a factor in the higher risk of delays in full breast-milk production, they speculate.

Whatever the underlying mechanisms for the findings, Nommsen-Rivers said that the bottom line for women is to seek help for any early breastfeeding difficulties.

She suggested that during pregnancy, women try to see a provider who has an affiliation with a lactation consultant. A home visit from the consultant in the first couple days after a woman gives birth can help identify and address any breastfeeding difficulties.

Women who feel their milk has not come in within 72 hours should call their pediatrician, Nommsen-Rivers said. The doctor can weigh and assess the baby, and watch the mother breastfeed to help spot any problems.

To help support early breastfeeding success, the American Academy of Pediatrics recommends that women ask to have their newborn placed in skin-to-skin contact with them immediately after birth so that they can breastfeed.

Frequent feedings in the early days are also important, Nommsen-Rivers said. It is often recommended that women breastfeed every two hours, but she suggested that new moms try to breastfeed whenever their newborn "shows an interest," with cues such as "smacking" his or her lips.

The rate of delayed milk production in this study — 44 percent — is significant, according to Nommsen-Rivers. Past studies have shown that compared with U.S. women, those in less-developed nations, such as Peru and Guatemala, tend to have their milk come in more quickly.

Pinning down the reasons for that difference — including the facets of modern maternity care that may be involved — will be important, Nommsen-Rivers said.