FRIDAY, March 13 (HealthDay News) -- The things that affect a woman's reproductive health can also have an effect on her heart, new research shows.

Giving birth prematurely or delivering a small-for-gestational-age baby are both associated with a later risk of cardiovascular disease in the mother, according to two studies expected to be presented Friday at an American Heart Association meeting in Palm Harbor, Fla.

A third study found that when women's ovaries were removed and the estrogen wasn't replaced through hormone therapy, a woman's overall risk of dying increased, as did her risk of dying of heart disease or stroke.

The first study looked for associations between gestational size, the timing of the birth and the risk of cardiovascular disease in more than one million Swedish women who'd given birth to their first baby after 1973. Only women who had singleton pregnancies were included in the analysis.

The researchers followed-up with the women for an average of 16 years, but for as long as 33 years.

They found that women who'd had a small-for-gestational-age baby or a preterm baby had a higher risk of cardiovascular disease, and that women who'd had both a small and preterm baby had a two to three times higher risk of cardiovascular disease later in life.

Dr. Erik Ingelsson, an associate professor of epidemiology at the Karolinska Institute, said that the increased risk appears to be lifelong.

"It seems like having a premature or small-for-gestational birth infant is a risk factor for cardiovascular disease, and thus, it is even more important to pay attention to the risk factors that you can affect, i.e., smoking cessation, eat healthy and avoid overweight and exercise more," said Ingelsson.

A second study, this one done with data from almost 435,000 births in Denmark, came to a similar conclusion. In this study, the births occurred from 1973 to 1983, and the later data on the moms came from medical records from 1977 to 2006.

More than 27,000 of the women had at least one preterm birth, and there were nearly 41,000 cases of cardiovascular disease in the whole study population.

The researchers found that women with a history of preterm birth had 40 percent higher odds of developing cardiovascular disease than women without such histories. Women who had more than one preterm birth had a threefold increased risk of dying from cardiovascular disease, the researchers found.

"We don't know exactly why the risks are increased. Our hypothesis is that these women may be coming into pregnancy a little bit different. It could be that what puts them at risk for preterm birth is also related to cardiovascular disease risk later," said the study's lead author, Janet Catov, an assistant professor in the department of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine.

But, she said, the researchers can't know the cause for sure from this data, only that there's an association.

"Women who've had preterm births might want to talk about it with their physicians, and make sure they know their numbers. What is your cholesterol? What about your LDL ['bad' cholesterol] ?," she said.

The third study looked at how having the ovaries removed (oophorectomy) at the time of a hysterectomy affected a woman's health. In this study of almost 30,000 women, 44 percent had a simple hysterectomy, which left their ovaries intact, while 56 percent had their ovaries removed along with their uterus.

After 24 years of follow-up, the researchers found that women who'd had their ovaries removed had lower rates of breast, ovarian and total cancers. However, the overall risk of dying (from any cause) was increased by 12 percent in woman who'd had their ovaries removed, and the rates of heart disease and stroke were increased by 17 and 14 percent, respectively. The odds of lung cancer jumped 26 percent higher in women whose ovaries were removed.

In women who didn't use estrogen replacement therapy, the results were even more dramatic. All-cause mortality rose by 40 percent, and the risk of heart disease and stroke were about twofold higher.

"In no analysis or age-group does oophorectomy increase survival," wrote the study's authors.

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Related MedlinePlus Pages:

• Childbirth
• Heart Disease in Women
• Hysterectomy