The last weeks of pregnancy are essential for infants’ health and development, and premature birth can have serious consequences. Expecting Massachusetts parents should be aware of the risk factors for preterm birth.

According to the Centers for Disease Control and Prevention, the number of infants born preterm—that is, before 37 weeks of gestation—actually increased between 2014 and 2015 following a decline during the previous seven years. The causes of this phenomenon are not yet clear.

Preterm infants have a higher risk of death compared to other babies. Premature infants also are more likely to have health problems and severe disabilities, including vision and hearing impairment, difficulties feed or breathing, cerebral palsy and developmental delay.

Fox News reported that approximately one in 10 infants are delivered prematurely. In many cases, the causes of preterm delivery are unknown; however, there are a number of factors that may increase the possibility of an early birth.

The mother’s medical history plays an important role. Women who suffer from depression or are underweight both face risks of premature birth. Interestingly, the father’s mental health may contribute; depression among fathers also leads to a higher chance of early delivery. Bacterial infections during pregnancy may increase the risk, too. Additionally, a shortened cervix resulting from a loop electrosurgical excision procedure can lead to preterm birth.

Apart from health factors, other pregnancy circumstances have been implicated in premature births. Women who become pregnant via in-vitro fertilization or soon after a previous pregnancy have a higher likelihood of delivering preterm. Multiple pregnancies result in premature delivery more commonly than do single pregnancies. Indeed, approximately half of all twin births occur preterm, and the number goes up for multiple pregnancies.

Out of all the risk factors, a history of previous preterm births perhaps plays the most significant role. Women who have delivered prematurely in the past do so again in 30 to 50 percent of subsequent pregnancies.