Older women are more likely to suffer from diabetes and high blood pressure during their pregnancies.
For the few women who manage to get pregnant after age 45, both they and their babies have a higher risk of complications, Israeli researchers have found.
For instance, they are about 3 times more likely than younger women to experience diabetes and high blood pressure during their pregnancies, the researchers report in the American Journal of Obstetrics & Gynecology.
Older women also have higher rates of pre-term births and placenta previa, in which the placenta blocks the opening to the birth canal.
"Increasing age leads to less (healthy) individuals, and less healthy individuals do have higher pregnancy risks," Dr. Maximilian Franz of the Medical University of Vienna, who did not participate in the study, told Reuters Health.
More women are delaying pregnancy today, causing experts to question whether there are any consequences to mother or child. Some studies have suggested older mothers fare worse, but others have found no differences. Still, most of the research has focused on women 35 and older, not those over 40.
To better understand the risks involved in such pregnancies, Dr. Yariv Yogev and colleagues at Tel Aviv University looked at how women of varying ages fared while giving birth at a local hospital between 2000 and 2008.
Among nearly 80,000 women who gave birth during that time, only 177 (0.2%) were 45 or older.
The majority of older women conceived using donor eggs, and 80% delivered their babies by Caesarean section - more than twice the overall rate.
Comparing older mothers to those 44 and younger, the researchers found that 17% and 6% were diabetic during their pregnancies, respectively.
9% of older mothers had high blood pressure while pregnant, a condition that affected less than 3% of mothers overall. Placenta previa occurred in nearly 6%, or about 6 times the overall rate.
Advanced age also appeared to shorten pregnancies. More than 1 in 5 of the older mothers delivered their babies at less than 37 weeks' pregnancy (a normal pregnancy lasts 40 weeks), compared to only 1 in 10 of all the women.
Older mothers were more likely to experience fever and severe bleeding after birth. On average, they and their newborns needed longer hospital stays, and the babies more often landed in the ICU. Some 4% of the newborns had metabolic problems such as low blood sugar, versus less than 2% of babies born to mothers of all ages.
For the 27 women who delivered at 50 years or older, the risks of complications and pre-term birth were even higher.
In an e-mail, Franz said it may not always be women's age per se that's the problem, but rather that the older people get, the more likely they are to have underlying diseases that can complicate pregnancy.
Many women used assisted reproductive technology, such as donor eggs, which can also carry risks, Franz noted. But since egg donors are typically young women, those pregnancies may actually be healthier than if women used their own eggs, which likely have more genetic abnormalities, he added.
The high caesarean rate among older mothers likely has several explanations, Franz said. There's the desire for a safe birth, as well as the higher rate of premature births and breech births, for example.
But previous research has also shown that older women may be more at risk of problems with the muscles of their uterus, suggesting the increased risk of caesarean delivery "is likely to have a biological basis."
Have you had a baby after 45? What was your experience?