4 - The periconceptional and embryonic period

Summary

Introduction

The periconceptional period of mammalian development has long been recognised as an early ‘developmental window’ during which environmental conditions may influence the pattern of future growth and physiology. For example, in early studies, it was found that in-vitro culture of mouse preimplantation embryos prior to transfer to recipient females lead to reduced fetal growth compared to in-vivo-derived fetuses (Bowman and McLaren 1970). The culture of ruminant embryos prior to transfer has also been linked with abnormal future growth and the so-called ‘large offspring syndrome’ (LOS), where fetal organomegaly is associated with perinatal mortality (reviewed in Sinclair et al. 2000). The concern from animal studies that preimplantation environment may alter embryo developmental potential has led to retrospective analysis of possible effects resulting from human in vitro fertilisation and assisted reproduction treatment (ART). Indeed, a number of ‘outcome’ studies in different parts of the world have identified a small increase in preterm delivery, low birthweight and perinatal mortality in singleton pregnancies following ART compared with that following natural conception (Hansen et al. 2002, Schieve et al. 2002).

The concept that embryo environment in vitro may modulate future development has been further expanded by a growing literature demonstrating that similar phenomena may occur in vivo, in response to maternal diet and physiological status. Thus, in rats, maternal low-protein diet administered exclusively during the preimplantation period caused abnormal postnatal growth and organ size and onset of high blood pressure in a gender-specific manner (Kwong et al. 2000).