New research finds that women who change partners between the births of their first two children are more likely to deliver pre-term babies with a low birth weight than women who have the same partner.
These babies are also more likely to die within the first year of life. The results are the same even when researchers take into account the mother's age and education, the interval between births, and the decades of birth.
Researchers speculate that women who change partners between births may belong to a selected group with characteristics that increase risk or they may change their lifestyle or behavior in ways that could negatively impact their pregnancy. They also cite risky behavior such as smoking or drinking during pregnancy and poor nutrition.
Researchers examined the records of nearly 2 million births between 1967 and 1998. During those 30 years, the proportion of women who changed partners between their first two births tripled, and more women had a higher-level education. Researchers say a change between partners is more likely in women with a low level of education than in women with a high level of education.
The researchers say the risk of infant mortality decreases from the first child to the second in women who have the same partner, but increases if a woman changes partners. The same trend holds true when comparing risks of delivering prematurely and having a baby with a low birth weight.
Researchers also looked specifically at a woman's level of education. They found that, for second births, the more education a mother has, the less likely she is to lose her baby during its first of life -- even if a woman changed partners. Pre-term birth and low birth weight were less common in women with more education, but only if they had the same partner. However, a high level of education does not seem to protect against premature delivery or low birth weight if she changes partners between births.