Acta Obstet Gynecol Scand 56: 491-493, 1977
A COMPARISON BETWEEN THE LECITHIN/SPHINGOMYELIN RATIO AND THE NILE BLUE SULPHATE TEST IN THE ESTIMATION OF FETAL MATURITY J. M. Gilbert, N. F. Taylor and I. R. McFadyen From the Northwick Park Hospital and Clinical Research Centre, Harrow, Middlesex, England
Abstract. Functional fetal maturity was assessed in 72 patients by measuring in amniotic fluid the lecithinlsphingomyelin ratio and the differential cell count. The correlation between these two tests is presented. Only one fetus with a lecithinlsphingomyelin ratio of 2 or more developed the respiratory distress syndrome after delivery: that was the child of a diabetic mother. The technical limitations of the lecithinlsphingomyelin ratio meant that it could not be measured in 12 % of samples obtained.
The L/S ratio of amniotic fluid is a measure of fetal pulmonary maturity. It is an index of the concentration of dipalmitoyl lecithin, which is the major surface active agent in the mature lungs (9). A baby born before it has the capacity to synthesize sufficient dipalmitoyl lecithin is likely to develop the respiratory distress syndrome (RDS). The Nile blue sulphate (NBS) test is thought to give a measure of the functional maturity of sebaceous glands (4). Cells from the glands are found in amniotic fluid and the percentage stained orange by the dye increases with gestational age. This paper compares the L/S ratio to the NBS test and examines their use in the management of a planned delivery.
PATIENTS AND METHODS The series comprises 72 consecutive patients in whom induction of delivery was contemplated. Seventy-five samples of amniotic fluid were collected by transabdominal amniocentesis. Each sample was evaluated by both the L/S ratio and the NBS test. The obstetric management of the patients was then conducted with full reference to the results obtained.
Lecithinlsphingomyelin ratio The LlS ratios were determined by a modification of the method of Gluck & Kulovich (9). Two ml of centrifuged amniotic fluid were submitted to solvent extraction and acetone precipitation. The extracts were chromatographed using the system of Coch and co-workers (2). The spots were visualized by spraying with 10% aqueous ammonium sulphate followed by chamng by heating at 250°C for 15 min. The lecithin and sphingomyelin spots were measured in two dimensions and the results were reported as “lecithin sphingomyelin area ratios”. By the use of standard dipalmitoyl lecithin and sphingomyelin a linear relationship was found between spot “size” and phospholipid concentration over the range normally encountered (10-100 pg). An L/S ratio of 2.0 or greater is said to indicate functional maturity of the fetal lungs. With ratios of less than 1.5 the incidence of significant respiratory distress is 100%. When the L/S ratio is 1.5-2.0, some patients develop respiratory distress, but much of it will be mild (7). Amniotic fluid cytology by the Nile blue sulphate stain All samples were analysed within 24 hours of being taken and interpreted according to the criteria of Husain & Sinclair (10) and Brosens &Gordon (1) (Table 1). “Clumping” of the cells is a technical problem which affects the cell counting, as recognized by Brosens & Gordon (1). In one case there was afall from I5 to 5 % orange staining cells in samples taken 2 weeks apart due to this effect. The neonates The maturity of all babies was assessed clinically by a member of the medical staff within 24 hours of birth.
RESULTS The results of the tests on the amniotic fluid samples are shown in Fig. 1. This indicates the correlation between the L/S ratio and the NBS test. Acta Obstet Gynecol Scund 56 (1977)
J . M . Gilbert et a l .
Table I. The interpretation of the N i l e blue sulphate test After Brosens & Gordon, 1966 Percentage of cells staining orange
Gestational age (weeks)
0-1 1-10 10-50 >50
0-34 34-38 3840 >40
The 72 mothers in the series were delivered of 74 babies, there being two sets of twins. The mean birthweight was 3.23 kg (7 Ib 2 oz) with a standard deviation of 0.4943 and a coefficient of skewness of 0.1697. This result does not differ significantly from the zero coefficient of skewness of a normal distribution (P