weight gain during pregnancy is extremely variable and can be influenced by factors such as maternal age, parity, BMI, diet, smoking, pre- pregnancy weight, size of the fetus, and maternal illness such as diabetes. The weight gain is distributed between the fetus, placenta, membranes, amniotic fluid, and the physiological development of maternal organs, e.g. uterus and breasts (blood and fat deposition in preparation for lactation). Most healthy women in the UK gain between 11 and 16kg, although young mothers and primigravidae usually gain more than older mothers and multigravidae.18
An optimal weight gain of 12.5kg is the figure used for an average nancy. This is associated with the lowest risk of complications during preg-nancy and labour and of low birthweight babies.19 Maternal weight gain tends to be more rapid from 20 weeks onwards, although excessive weight gain during pregnancy is associated with post- partum weight retention, as is increased weight gain in early pregnancy compared with late pregnancy.
weight gains above 12.5kg in women of normal pre- pregnancy BMI are unlikely to reflect an increase in fetal weight, maternal lean tissue, or water.
Perinatal outcome has a complex relationship with maternal pre- pregnancy BMI, as well as with antenatal weight gain. Calculating the BMI is a method of estimating the amount of body fat, based on the weight and height. The index is calculated by dividing the individual’s weight in kilograms by the square of his or her height in metres. Many charts are available for instant grading.
The wHO20 has defined BMI classifications to represent the risk of asso-ciated co- morbidities (Table 5.1).
Weight gain for individual women
Recommended weight gain should be based on the pre- pregnancy BMI (Table 5.2), as lower perinatal mortality rates are associated with under-weight women who achieve high under-weight gains and overunder-weight women who achieve low gains. The number of women in the obese category of BMI
Table 5.1 BMI classification
Classification BMI (kg/ m2) Risk of co- morbidities Underweight <18.5 Low, but the risk of other
clinical problems is increased
Ideal range 18.5– 24.9 Average
Overweight 25.0– 29.9 Mildly increased
Obese >30.0 Increased
Class I (moderately obese) 30.0– 34.9 Moderate Class II (severely obese) 35.0– 39.9 Severe Class III (morbidly obese) >40.0 very severe
weIGHT GAIN IN PReGNANCY AND BODY MASS INDeX 95
is escalating and rapidly becoming a major public health problem within maternity care.21 Maternal and perinatal complications are much more prevalent such as an increased risk of gestational diabetes, pre- eclampsia, macrosomia, and perinatal mortality.21,22
Weight management in pregnancy
During and after pregnancy are vulnerable life stages for weight gain, which makes them a good time for health- care professionals to discuss diet and physical activity. Dieting during pregnancy is not recommended, as weight loss may harm the health of the unborn child. But there are no guidelines on recommended weight gain in the UK which are broken down by pre- pregnancy BMI category.
• The British Dietetic Association23 recommends that pregnant women should gain at least 6kg if overweight.
• The USA Institute of Medicine24 recommends that obese women should gain between 5 and 9kg over the course of their pregnancy.
Pregnancy after weight loss surgery
The prevalence of obesity among women of reproductive age is 19%.25 As four times as many women have weight loss surgery than men, there are a growing number of women presenting for antenatal care having had weight loss surgery. women are advised not to become pregnant within 12 months of having had weight loss surgery. Despite this advice, many women do become pregnant and go on to have a successful pregnancy.
There are various surgical procedures available. A full description is available from the NHS website (available at: M www.nhs.uk/ conditions/
weight- loss- surgery/ Pages/ Introduction.aspx). Procedures are either restrictive (gastric band, sleeve gastrectomy) or malabsorptive (biliopan-creatic diversion (BPD), duodenal switch (DS)) or have an element of both (Roux- en- Y gastric bypass).
Antenatal care after weight loss surgery should consider
• Nutritional deficiencies can occur after bariatric surgery and it is usual for all patients to be prescribed multivitamin and mineral supplements, and sometimes at higher doses than usually observed in the general population.
Table 5.2 weight gain in pregnancy and BMI Pre- pregnancy BMI
[weight (kg)/ height (m2)] Recommended weight gain
(kg) (lb)
Low (<19.8) 12.5– 18.0 28– 40
Normal (19.8– 26) 11.5– 16.0 25– 35
High (26.0– 29.0) 7– 11.5 15– 25
Obese (>29) 6 (min) 14 (max)
• A higher level of folic acid (5mg) and a vitamin D supplement are also advised during pregnancy.
• women who had bypass surgery are at the greatest risk of nutritional deficiencies, particularly vitamin D, calcium, vitamin B12, and iron, and they should be monitored closely during their pregnancy for nutritional deficiencies.
References
18 webster- Gandy J, Madden A, Holdsworth M (2006). Oxford Handbook of Nutrition and Dietetics.
Oxford: Oxford University Press.
19 Hytten fe (1991). weight gain in pregnancy. In: Hytten fe, Chamberlain G, eds. Clinical Pathology in Obstetrics. London: Blackwell Scientific, pp. 173– 203.
20 world Health Organization (2000). Obesity: Preventing and Managing the Global Epidemic: Report of a WHO Consultation (WHO Technical Report Series 894). Geneva: world Health Organization.
21 veerareddy S, Khalil A, O’Brien P (2009). Obesity implications for labour and the puerperium.
Br J Midwifery 17: 360– 2.
22 Stewart fM, Ramsay Je, Greer IA (2009). Obesity: impact on obstetric practice and outcome.
Obstet Gynaecol 11: 25– 31.
23 British Dietetic Association (2016). Food fact sheet: pregnancy. London: British Dietetic Association. Available at: M www.bda.uk.com/ foodfacts/ pregnancy.pdf.
24 Institute of Medicine (2009). Weight Gain during Pregnancy: Re- examining the Guidelines.
washington DC: US Department of Health and Human Services.
25 Centre for Maternal and Child enquiries (CMACe) (2010). Maternal obesity in the UK; findings from a national project. London: CMACe. Also available at: M www.publichealth.hscni.net/ sites/
default/ files/ Maternal%20Obesity%20in%20the%20UK.pdf.
Further reading
Goldberg GR (2000). Nutrition in pregnancy. Advisa Medica (London) 1: 1– 3.
National Institute for Health and Care excellence (2006). Obesity prevention. NICe guidelines CG43.
Available at: M www.nice.org.uk/ guidance/ cg43.
National Obesity Observatory (2010). Bariatric surgery for obesity. Available at: M www.noo.org.
uk/ uploads/ doc/ vid_ 8774_ NOO%20Bariatric%20Surgery%20for%20Obesity%20fINAL%20 MG%20011210.pdf.
UK Obstetric Surveillance System (2015). Pregnancy following gastric bypass surgery: study protocol.
Available at: M www.npeu.ox.ac.uk/ ukoss/ current- surveillance/ gby.
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