Project overview
Our main aim is to determine how maternal diet, before and during pregnancy, enables optimal fetal growth. Our objectives are to: i) study 90 non pregnant and 90 pregnant women from the Southampton Womens Survey (SWS), ii) investigate some 30 of these women but before and twice during pregnancy, iii) measure height, weight and body composition (proportion of fat, lean and visceral tissue), whole body protein turnover (a measure of the body¿s capacity to synthesise and break down protein) and urea production (a measure of loss of amino acids by oxidation) in these women. We will send a letter and information sheet to non pregnant women interviewed in the SWS who said that they anticipate trying for a baby within 12 months. If they agree to take part we will arrange to carry out the metabolic studies. Subsequently we will follow them up for as long as possible but so that, in those women who become pregnant, neonatal anthropometry is complete 3 months before the end of the project. We expect about 30 women will become pregnant during follow up. We will also recruit 60 women from the SWS during pregnancy only when they attend the SWS ultrasound unit at 11 weeks gestation. Recruiting women from the SWS allows us to use information previously collected in both non pregnant and pregnant women on diet, sociodemographic factors, body composition, and ultrasound measures of fetal size. Protein metabolism will be assessed as follows using protocols that we routinely use: 1 protein synthesis and breakdown (protein turnover) will be determined using stable isotope techniques. Protein synthesis will be estimated from nitrogen flux, which is determined from the labelling of urea and ammonia with 15N in a 24 hour urine collection after a single oral dose of 15N labelled glycine. 2. Amino acid oxidation will be determined from the labelling of urea with 15N in a 48 hour urine collection following a single oral does of 15N15N urea. Total urine volume will be recorded at the end of each 24 hour period and aliguots stored frozen for analysis. Urinary ammonia and urea concentration will be measured by the Berthelot method. Ammonia and urea nitrogen will be extracted for mass spectrometry by alkaline aeration or with the use of a short ion-exchange column, and nitrogen gas will be generated by reaction with alkaline hypobromite. Enrichment of 15N in urinary ammonia and urea will be measured in a triple collector isotope ratio mass spectrometer. Each non pregnant women will be asked to complete both protocols one month apart at around day 4-10 of the menstrual cycle. Each pregnant woman will be asked to complete both protocols, a week apart, twice during pregnancy (13 and 14 and 34 and 35 weeks gestation). We will also assess body composition once in non pregnant women and twice in pregnant women using anthropometric techniques. Body fat will be estimated from the measurement of four skinfold thicknesses, muscle mass from 24 hour creatinine excretion, and lean body mass and visceral mass by difference from body weight.