Frequently Asked Questions

Q) What is the difference between embryological age and gestational age?

A) Embryological age is the true age of the foetus, with Day 1 being the day of fertilisation. As it is impossible to accurately pinpoint which day this is, it is common to use gestational age in the clinical setting. The first day of foetal life using this time scale is the last menstrual period (LMP), which is approximately 14 days before fertilisation. Embryological age is expressed in days (e.g. Day 18) and gestational age is expressed in weeks completed after the last period plus days (e.g. 4 weeks 2 days). Remember when converting between ages that gestational age is always an extra two weeks longer than embryological age. All ages described throughout this website are based on embryological age.

Gestational Age

Two weeks are added onto embryological age to calculate gestational age
Q) What is an ectopic pregnancy?

A) An ectopic pregnancy occurs when the fertilised oocyte implants somewhere other than the endometrium. This is usually in the fallopian tube, and is very dangerous to both mother and foetus as it may result in death. If left untreated the fallopian tube will rupture when the foetus becomes large enough, causing internal haemorrhage in the mother which is a medical emergency.

Ectopic pregnancy
An ectopic pregnancy in the fallopian tube

Q) Where does the zygote get nutrition from during the first week of development?

A) The zygote acquires its nutrients via passive diffusion from secretions made by endometrial glands. Although small in volume and nutritional value, these secretions provide enough energy for the first week of life whilst the zygote is still a small bundle of cells which require a tiny amount of energy.

Endometrial secretion
A scanning electron micrograph of a secretion (pink) from an endometrial gland (green)

Q) What is pre-eclampsia?

A) Pre-eclampsia is a condition which can develop in the second half of pregnancy, and is characterised by high blood pressure, oedema, and the appearance of protein in the mother’s urine. The condition restricts foetal growth and modifies the mother’s vasculature. It has several causes including cigarette smoking and obesity, and if left untreated can develop into the very dangerous condition called eclampsia (seizures during pregnancy) – labour may have to be induced to save the lives of both mother and baby. Aspirin and calcium supplements may be given early in pregnancy to prevent pre-eclampsia.


Spiral arteries of the endometrium in various conditions
Q) What is neonatal respiratory distress syndrome (NRDS)?

A) NRDS occurs when a baby is born very prematurely, meaning its lungs have not fully matured yet. As the lungs are not fully developed, not enough surfactant has been produced which means the alveoli are liable to collapse and gas diffusion across the alveolar membrane is poor – resulting in hypoxia in the baby. The baby will have rapid shallow breathing and will appear blue (cyanosis) due to the lack of oxygen in the blood. Treatment is intensive care therapy and administration of warm moist oxygen while the lungs finish developing.

Normal alveoli on the left, immature alveoli on the right

Q) What causes the newborn baby to take its first breath?

A) Multiple stimuli trigger the newborn to take its first breath. There is the mechanical pressure exerted on the baby during labour, and the cold shock as it transfers from the warm wet environment of the uterus to the comparatively cold outside world. Light also acts as a stimulus to initiate the reflex of taking the first breath, and once placental circulation is stopped the blood gases in the newborn’s circulation change which helps stimulate breathing.

First breath

A baby taking it's first breath
Q) What is a patent foramen ovale (PFO)?

A) A patent foramen ovale is a heart defect in which the foramen ovale, the hole between the left and right atria, fails to close after birth (once the first breath is taken). The shunt persists and allows oxygenated blood in the left atrium to mix with deoxygenated blood in the right atrium, which results in a lower oxygen concentration throughout the circulatory system. The condition is relatively common (10-20% of adults) and is usually asymptomatic.

Patent Foramen Ovale (PFO)

Q) What effect does drinking alcohol and smoking cigarettes have on the foetus?

A) Consuming substances whilst pregnant will affect the baby as the drug molecules will cross the placenta and enter the foetus. Smoking cigarettes increase the risk for a number of complications including pre-eclampsia, premature birth, miscarriage, low birth weight, birth defects such as cleft palate, and intra-uterine growth restriction (IUGR). Drinking lots of alcohol increases the risk for a condition known as fetal alcohol syndrome (FAS) which has a long list of problems including intra-uterine growth restriction, heart defects, and mental retardation.

Twins, the left of which has suffered from intra-uterine growth restriction (IUGR)