This is an account of further work on a rating scale for depressive states, including a detailed discussion on the general problems of comparing successive samples from a 'population', the meaning of factor scores, and the other results obtained. The intercorrelation matrix of the items of the scale has been factor-analysed by the method of principal components, which were then given a Varimax rotation. Weights are given for calculating factor scores, both for rotated as well as unrotated factors. The data for 152 men and 120 women having been kept separate, it is possible to compare the two sets of results. The method of using the rating scale is described in detail in relation to the individual items. rotated by the Varimax method (Kaiser, 1958). Finally, weights were computed so that factor scores could be calculated from the raw scores on the rating scales.

Singletons pregnancies after IVF/ICSI are associated with higher risks of obstetric and perinatal complications when compared with spontaneous conception. Further research is needed to determine which aspect of assisted reproduction technology poses most risk and how this risk can be minimized.

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The results of this cumulative meta-analysis confirm that the decreased risks of small for gestational age, low birth weight and preterm delivery and increased risks of large for gestational age and high birth weight associated with pregnancies conceived from frozen embryos have been consistent in terms of direction and magnitude of effect over several years, with increasing precision around the point estimates. Replication in a number of different populations has provided external validity for the results, for outcomes of birth weight and preterm delivery. Meanwhile, caution should be exercised about embarking on a policy of electively freezing all embryos in IVF as there are increased risks for large for gestational age babies and hypertensive disorders of pregnancy. Therefore, elective freezing should ideally be undertaken in specific cases such as ovarian hyperstimulation syndrome, fertility preservation or in the context of randomised trials.

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