What is the issue?
Does dietary advice or supplementation to increase energy and protein intake in pregnancy improve outcomes for babies, and are there any adverse effects? Do these interventions impact differently on poorly-nourished and well-nourished pregnant women and their infants?
Why is this important?
During pregnancy, a baby developing inside the womb receives all its nutrition from its mother. Inadequate dietary intake during pregnancy can lead to malnutrition and poor outcomes for the baby. Therefore, advising women on their diet and providing food supplements in pregnancy may help babies to grow and thrive.
What evidence did we find
This review includes 17 randomised controlled trials, involving 9030 women. The quality of the included trials is low to moderate. We, examined several aspects of dietary advice and supplementation and produced the following four main findings.
(1) Providing nutritional advice resulted in an increase in the mother's protein intake, there were fewer babies born too early (two trials involving 449 women) and fewer babies with low birthweight (one trial involving 300 women), One study of 389 women showed increases in some babies birth head circumference (in one trial involving 389 women) There were also more babies with a higher birthweight among undernourished women (two trials involving 320 women).
(2) Giving the mothers balanced energy and protein supplements was associated with fewer babies dying during labour (five trials, 3408 women), clear increases in birthweight (11 trials, 5385 women) and fewer babies who were small-for-gestational age (seven trials, 4408 women). However, the impact on the long-term health of the baby was uncertain, including among undernourished women.
(3) High-protein supplementation (one trial involving 1051 women) showed no benefit for women and potential harm for the baby through an increase in the number of babies small for their gestational age at birth.
(4) Isocaloric protein supplementations (i.e. balanced supplements in which the protein replaces an equal quantity of other nutrients, e.g. fat and carbohydrate): in birthweight and weekly gestational weight gain, showed no benefit for women or their babies (two trials involving 184 women).
What does this mean?
Providing nutritional advice or balanced energy and protein supplements to women during pregnancy may be beneficial. However, there is not enough evidence on isocaloric protein supplements which currently appear to be unhelpful and high-protein supplements may be harmful.
This review provides encouraging evidence that antenatal nutritional education with the aim of increasing energy and protein intake in the general obstetric population appears to be effective in reducing the risk of preterm birth, low birthweight, increasing head circumference at birth, increasing birthweight among undernourished women, and increasing protein intake. There was no evidence of benefit or adverse effect for any other outcome reported.
Balanced energy and protein supplementation seems to improve fetal growth, and may reduce the risk of stillbirth and infants born small-for-gestational age. High-protein supplementation does not seem to be beneficial and may be harmful to the fetus. Balanced-protein supplementation alone had no significant effects on perinatal outcomes.
The results of this review should be interpreted with caution. The risk of bias was either unclear or high for at least one category examined in several of the included trials, and the quality of the evidence was low for several important outcomes. Also, as the anthropometric characteristics of the general obstetric population is changing, those developing interventions aimed at altering energy and protein intake should ensure that only those women likely to benefit are included. Large, well-designed randomised trials are needed to assess the effects of increasing energy and protein intake during pregnancy in women whose intake is below recommended levels.
Gestational weight gain is positively associated with fetal growth, and observational studies of food supplementation in pregnancy have reported increases in gestational weight gain and fetal growth.
To assess the effects of education during pregnancy to increase energy and protein intake, or of actual energy and protein supplementation, on energy and protein intake, and the effect on maternal and infant health outcomes.
We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2015), reference lists of retrieved studies and contacted researchers in the field.
Randomised controlled trials of dietary education to increase energy and protein intake, or of actual energy and protein supplementation, during pregnancy.
Two review authors independently assessed trials for inclusion and assessed risk of bias. Two review authors independently extracted data and checked for accuracy. Extracted data were supplemented by additional information from the trialists we contacted.
We examined 149 reports corresponding to 65 trials. Of these trials, 17 were included, 46 were excluded, and two are ongoing. Overall, 17 trials involving 9030 women were included. For this update, we assessed methodological quality of the included trials using the standard Cochrane criteria (risk of bias) and the GRADE approach. The overall risk of bias was unclear.
Nutritional education (five trials, 1090 women)
Women given nutritional education had a lower relative risk of having a preterm birth (two trials, 449 women) (risk ratio (RR) 0.46, 95% CI 0.21 to 0.98, low-quality evidence), and low birthweight (one trial, 300 women) (RR 0.04, 95% CI 0.01 to 0.14). Head circumference at birth was increased in one trial (389 women) (mean difference (MD) 0.99 cm, 95% CI 0.43 to 1.55), while birthweight was significantly increased among undernourished women in two trials (320 women) (MD 489.76 g, 95% CI 427.93 to 551.59, low-quality evidence), but did not significantly increase for adequately nourished women (MD 15.00, 95% CI -76.30 to 106.30, one trial, 406 women). Protein intake increased significantly (three trials, 632 women) (protein intake: MD +6.99 g/day, 95% CI 3.02 to 10.97). No significant differences were observed on any other outcomes such as neonatal death (RR 1.28, 95% CI 0.35 to 4.72, one trial, 448 women, low-quality evidence), stillbirth (RR 0.37, 95% CI 0.07 to 1.90, one trial, 431 women, low-quality evidence), small-for-gestational age (RR 0.97, 95% CI 0.45 to 2.11, one trial, 404 women, low-quality evidence) and total gestational weight gain (MD -0.41, 95% CI -4.41 to 3.59, two trials, 233 women). There were no data on perinatal death.
Balanced energy and protein supplementation (12 trials, 6705 women)
Risk of stillbirth was significantly reduced for women given balanced energy and protein supplementation (RR 0.60, 95% CI 0.39 to 0.94, five trials, 3408 women, moderate-quality evidence), and the mean birthweight was significantly increased (random-effects MD +40.96 g, 95% CI 4.66 to 77.26, Tau² = 1744, I² = 44%, 11 trials, 5385 women, moderate-quality evidence). There was also a significant reduction in the risk of small-for-gestational age (RR 0.79, 95% CI 0.69 to 0.90, I² = 16%, seven trials, 4408 women, moderate-quality evidence). No significant effect was detected for preterm birth (RR 0.96, 95% CI 0.80 to 1.16, five trials, 3384 women, moderate-quality evidence) or neonatal death (RR 0.68, 95% CI 0.43 to 1.07, five trials, 3381 women, low-quality evidence). Weekly gestational weight gain was not significantly increased (MD 18.63, 95% CI -1.81 to 39.07, nine trials, 2391 women, very low quality evidence). There were no data reported on perinatal death and low birthweight.
High-protein supplementation (one trial, 1051 women)
High-protein supplementation (one trial, 505 women), was associated with a significantly increased risk of small-for-gestational age babies (RR 1.58, 95% CI 1.03 to 2.41, moderate-quality evidence). There was no significant effect for stillbirth (RR 0.81, 95% CI 0.31 to 2.15, one trial, 529 women), neonatal death (RR 2.78, 95% CI 0.75 to 10.36, one trial, 529 women), preterm birth (RR 1.14, 95% CI 0.83 to 1.56, one trial, 505 women), birthweight (MD -73.00, 95% CI -171.26 to 25.26, one trial, 504 women) and weekly gestational weight gain (MD 4.50, 95% CI -33.55 to 42.55, one trial, 486 women, low-quality evidence). No data were reported on perinatal death.
Isocaloric protein supplementation (two trials, 184 women)
Isocaloric protein supplementation (two trials, 184 women) had no significant effect on birthweight (MD 108.25, 95% CI -220.89 to 437.40) and weekly gestational weight gain (MD 110.45, 95% CI -82.87 to 303.76, very low-quality evidence). No data reported on perinatal mortality, stillbirth, neonatal death, small-for-gestational age, and preterm birth.