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Table 1 Risk factors associated with an increased risk of preterm birth and the effectiveness of intervention arrayed according to the strength of evidence

From: Born Too Soon: Care before and between pregnancy to prevent preterm births: from evidence to action

  

How great is the risk?

Pregnancy in adolescence

+

Increased prevalence of anemia, pregnancy-induced hypertension, low birthweight, prematurity, intra-uterine growth retardation and neonatal mortality

Birth spacing

+

 

Short intervals

 

PTb: OR 1.45, LBW: OR 1.65

Long intervals

 

PTb: OR 1.21, LBW: OR 1.37

Pre-pregnancy weight status

+

 

Underweight

 

PTb: OR 1.32, LBW: OR 1.64

Overweight & obesity

 

PTb: OR 1.07

  

Maternal overweight is a risk factor for many pregnancy complications including hypertensive disorders, gestational diabetes, postpartum hemorrhage, stillbirth, congenital disorders

Both underweight and overweight women have a higher chance for requiring obstetric intervention at delivery

Micronutrient deficiencies

+/-

 

Folic acid

 

Folic acid deficiency is definitively linked to neural tube defects (NTDs) in newborns

Iron

 

Anemia increases the risk for maternal mortality, low birthweight, preterm birth and child mortality

Chronic diseases

+

 

Diabetes mellitus

 

Babies born to women with diabetes before conception have a much higher risk of stillbirths, perinatal mortality, congenital disorders, as well as spontaneous pregnancy loss, preterm labor, hypertensive disorders, and delivery by cesarean birth.

Hypertension

  

Anemia

 

A study shows that anemia before conception increases the risk of low birthweight (OR 6.5)

Poor mental health (especially depression) and Intimate partner violence

++

Increased risk for preterm birth, low birthweight and depression during pregnancy and the postpartum period

IPV-PTb OR 1.37, LBW OR: 1.17

Also increased risk for spontaneous pregnancy loss, stillbirth, gynecological problems including sexually-transmitted infections, depression

Infectious diseases

++

 

STIs - syphilis

 

Infectious diseases increase the risk for spontaneous pregnancy loss, stillbirths and congenital infection

HIV/AIDS

  

Rubella

  

Tobacco use

++

A single study shows risk PTb OR: 2.2

Smoking increases the risk for spontaneous pregnancy loss, placental disorders, congenital malformations, sudden infant death syndrome, stillbirths and low birth weight

  1. For magnitude of risk:
  2. ++ means strong evidence of risk and implicated in biological pathways leading to preterm birth and low birthweight
  3. + means moderate evidence of risk on preterm birth and low birthweight
  4. +/- means weak evidence of risk on preterm birth and low birthweight
  5. Acroynms used: PTb = preterm birth; OR = odds ratio; IPV = intimate partner violence
  6. Source: Barros et al., 2010; Bhutta et al., 2011a; Goldenberg et al., 2008; Iams et al., 2008