F. E. Hytten

THE ASSESSMENT OF FETAL GROWTH

THE importance of low birthweight i n determining perinatal mortality, and as a possible cause of higher morbidity and impaired development during childhood, has been widely recognized. Two main categories of low birthweight babies ---those whose fetal growth rate has been normal but whose gestational age is short; and the “light for dates” baby, whose prenatal growth has probably been impaired-have been recognized to have different prognoses (e.g. Van den Berg and Yerushalmy, 1966). The assessment of fetal growth in the individual case involves the use of standards which describe the distribution of birthweights at given gestational ages. Neligan (1 965) and Gruenwald (1966) have reviewed most of the published work and have produced standards of their own. Most of the available standards are unsatisfactory in one way or another, either because the sample on which they were based was atypical, or because inaccuracies in the data gave rise to features which are likely to be “unbiological”. For example, both Neligan and Gruenwald found that the distributions of birthweights at early gestational ages showed evidence of bimodality, which they attributed to a proportion of cases in which the gestational ages had been underestimated. Both authors suggested, and Gruenwald applied, a correction which was based on the assumption that birthweights are symmetrically distributed around the principal mode of each bimodal distribution. Other investigators have used other devices to limit improbabilities in their data. Thus, Lubchenco, Hansman, Dressler and Boyd (1963) simply discarded infants whose birthweights were “not compatible” with their gestational ages; and McKeown and Gibson (1951) rejected the lowest and highest 1 per cent of values when birthweights were distributed by gestation within each pound (453 g.) of weight. This report is based on an analysis of 52,004 legitimate, single births which took place in the City of Aberdeen during the years 1948--64. The material is of exceptional value for the following reasons. Clinical records of all the births in a well-defined, socially variegated but ethnically rather homogeneous urban population were available. About 95 per cent of the inhabitants of Aberdeen were born in Scotland, the great majority in the northeast region. During the years under review, more than 80 per cent of Aberdeen births took place in one teaching maternity hospital, which was also responsible for the antenatal care of its booked patients. Most of the information on menstrual dates was collected by senior members of the obstetrical staff, many of whom were using the clinical records for research purposes. Finally, the heights and weights of nearly all the mothers were recorded, so that the influence of maternal size on birthweight could be investigated.

Boys and girls

The chances of a boy being born, rather than a girl, has a significance which varies from its importance for an individual mother or family, to the more disinterested curiosity of the epidemiologist who sees the statistical probability as a revealing biological variable. The sex ratio, the number of males per 100 females, changes throughout life (Hytten & Leitch 1971). It would appear that a considerably greater number of females than males are conceived but there is a conspicuous excess of females among very early spontaneous abortions so that by the end of the first trimester there are probably about 120 male fetuses for every 100 females. From that point male mortality always outstrips the loss of females. Excess male representation in late abortions and stillbirths reduces the sex ratio at birth to about 105 to 107 in mast European populations and further male losses in childhood reduces it to about 100, where it remains between the ages of about 20-50 years. Biologically that is what matters, because equality during the years of childbearing ensures the smallest likelihood of inbreeding. Beyond middle age male mortality again exceeds mortality in women so that by old age only 20 to 30 men remain for every 100 women. As generally used the term ‘sex ratio’ refers to the secondary sex ratio, the sex ratio at birth. A large literature has shown a wide variety of circumstances to be associated with variation in the sex ratio. So called ‘genetic’ determinants include differences with blood group of the mother. the alleged tendency of some families to have childre of only one sex and differences associated wit different population groups. There would appear t be a slight but real tendency for mothers of blood group AB to have more boys but whether there is a familial tendency to produce children of one sex is i

Clinical and Chemical Studies in Human Lactation

Methods of collecting samples of breast milk for the study of human lactation have many drawbacks. Ideally removal of breast milk from the mother should be such that not only is all the milk taken from the breast but also normal milk production is not disturbed. The humalactor is a recently devised breast pump which mechanically mimics the suckling action of the babys mouth. It has many advantages over manual milk expression in terms of comfort and effectiveness. The technique is standardized and does not depend on skilled operators. Furthermore the patients are willing to undergo a subsequent 24-hour sampling when the initial sampling has been easy and comfortable. A comparison of both methods (humalactors and manual expression by hand) was made in a series of 83 subjects studied in 1948-9 and in 85 subjects from a current study. In the 1st series the mean 7th day yield (representing result of manual expression) was 379.6 ml and the 6th day (computed from test weighings and measured strippings) 441.3 ml. Reduction of 61.7 ml is statistically significant at the 5% level. In the 2nd series the 7th-day yield (made by the humalactor) averaged 445 ml; the 6th day (computed again from test weighings and measured stripping) 419.8 ml. The difference 25.2 ml was not statistically significant but represented an increase nevertheless. No significant differences were observed in the fat content of the 7th-day milk in the 2 series. The findings suggest that manual expression yields a lesser amount of milk than the humalactor.

Intrauterine growth retardation: let's be clear about it

In clinical practice, fetal growth is confused with fetal size and it is common for «birthweight-for-gestational-age» standards to be described as «fetal growth charts», and a weight-for-gestation below some arbitrary centile to be referred to as «intrauterine growth retardation». The distinction between size and growth is critical. What the clinician needs to know is whether fetal growth has deviated from its normal progression

The weight of the placenta in relation to birthweight.

MATERIAL AND METHODS The analysis of birthweights was based on the records of 52,004 legitimate, single births in the City of Aberdeen during the years 1948-64. Cases of uncertain gestational age, macerated fetuses and perinatal deaths from malformations were excluded. For present purposes, we have also excluded domiciliary births, for which placental weights were seldom available, and fourth or later pregnancies, a high proportion of which were domiciliary births. Analyses involving certain clinical data could not be undertaken on births before 1958. Placentas were weighed routinely by the delivery room staff, without special preparation. Weights (originally recorded in pounds and ounces) therefore include attached cord and membranes and any contained blood or adherent blood clot. Data from the case records were summarized on Hollerith punch cards. Since birthweights were grouped in half-pound (227 8.) and placental weights in 2 oz. (57 g.) categories, it was impossible to obtain from the cards exact placental weight/birthweight ratios in individual cases and only the ratios of means are reported. The results described below do not suggest that it would be profitable to go back to the original case records in order to obtain more detailed information. Gestational ages are expressed in completed weeks, e.g. “39 weeks” includes all deliveries from 273 to 279 days, inclusive.

TOTAL BODY WATER IN NORMAL PREGNANCY

BODY water increases during pregnancy as a result of water in the foetus, the placenta and the liquor amnii, and because the organs of reproduction and the maternal blood volume enlarge. Clinical oedema occurs not uncommonly, and suggests that there is also an increase of extracellular water. Increased body water accounts for a large proportion of weight gained during pregnancy. Given more precise and extensive information, we could make more exact assessments of the components of weight gained during pregnancy and would be able to examine more rationally the basis of treatment aimed at reducing the amount of weight gained. Only a few estimates have been published hitherto, and these have been based on differences between measurements in late pregnancy and those made after parturition. Measurements made during the course of pregnancy are scanty and inadequate. Table I summarizes prekious findings. Those of Hutchinson et al. (1954), Haley and Woodbury (1956) and McCartney et al. (1959) agree in pointing to an average increase of about 6 litres, but only 12 subjects in all were studied, and the comparisons were between body water measured during late pregnancy or in labour and that measured 1 to 8 weeks after delivery. The “increases” in individuals range from 0 to 14.2 litres. The two investigations of Seitchik and his colleagues (1956, 1963) gave results which disagreed with each other and with those of other workers,

THE EPIDEMIOLOGY OF OEDEMA DURING PREGNANCY

THE interpretation of oedema during pregnancy is difficult, especially when it is not accompanied by other evidence of pre-eclampsia. It is doubtful if many obstetricians would support the extreme view of Cosgrove (1950): “. . . any degree of edema, even that manifested only by excessive weight gain is essentially abnormal, unphysiological and dangerous, necessitating alert attention and active therapy.” According to Greenhill (1965): “. . . mild edema unassociated with other symptoms . . . is of no special significance”, while Kellar (1959) considered that: “Oedema of the ankle region is very common in normal pregnancy and it is very difficult to say when this has passed the physiological limit.” In Kellar’s view therefore, the hydration of pregnancy may sometimes become manifest as oedema without being unphysiological. Our own interest in this subject was aroused during a study of the gain in total body water in women with normal pregnancies (Hytten, Thomson, and Taggart, 1966). None had hypertension or proteinuria, but a high proportion (46 out of 93) exhibited some oedema, usually of minor degree, but occasionally quite severe. It was not clear whether this should be regarded as unusual; we could find no published study of the incidence of oedema in normal and abnormal pregnancies. A study of the records of the Aberdeen Maternity Hospital was accordingly undertaken.

The energy cost of human lactation.

A total of 55 diet surveys were made on 49 women in Scotland within about 2 months of parturition some of whom were fully breast-feeding and some of whom were fully bottle-feeding their babies in an attempt to measure the effect of lactation on energy exchanges in the mother. 23 women were breast-feeding and 32 were bottle-feeding their babies; the lactating mothers took 591 kcal per day more than those who were not lactating. Both groups of mothers were losing weight and the estimated contribution of such losses to the total energy supply was added to and the amounts expended on basal metabolism deducted from the dietary energy intakes. The activity of each group was fairly similar; hence it was concluded that the average amount of energy available to support lactation was 618 kcal daily. The average energy value of the milk produced was estimated from the weights of the babies to be 597 kcal daily. From these data it was concluded that the energy exchanges in human lactation have an efficiency of 90% or more with the lower limit being 80%. Therefore an additional supply of 600 kcal in a daily diet should support lactation and 500 kcal is offered as the official recommended allowance.

THE AMINOACIDURIA OF PREGNANCY

The concentration of free amino acids in plasma and their excretion in urine was measured serially in ten healthy women during pregnancy and again postpartum. Almost all amino acids were excreted in greater amounts during pregnancy than in the non‐pregnant state and there appeared to be three definable patterns. The excretion of the five amino acids lost in greatest amount, glycine, histidine, threonine, serine and alanine, increased rapidly in early pregnancy to three or four times the non‐pregnant rate and continued to increase as pregnancy proceeded. For seven others: lysine, cystine, taurine, tyrosine, phenylalanine, valine and leucine, there was also a greatly increased excretion in early pregnancy, but there after excretion tended to fall. The remaining six amino acids measured showed little or no increase in excretion.

THE EXCRETION OF GLUCOSE DURING NORMAL PREGNANCY

Thirty healthy pregnant women took part in a serial study in which they collected 24‐hour samples of urine for the estimation of glucose excretion at least 8 times during pregnancy and again post partum; for one week before the collection they tested their urine with “Clinistix” each time they passed it. Ten of the women showed no obviously increased glucose excretion during pregnancy. The other twenty excreted glucose in above normal amounts but with great variation both from subject to subject and in the same subject. The pattern of excretion shown by “Clinistix” was one of intermittent glycosuria. Days and groups of days in which glycosuria was the rule were separated by similar periods without it. The value of routine urine testing for glucose in pregnancy is questioned.