In the UK, as many as 30-40% of pregnancies that end in childbirth are unplanned, while the number of children born after assisted reproductive technologies is growing every year.

It is already known that children born after a prolonged time to conception or assisted reproduction are at greater risk of poor health outcomes, such as preterm birth, low birth weight, and congenital anomalies, and some researchers have reported lower cognitive (mental) scores in such children.

Unplanned pregnancies also have poorer outcomes, but there has been little research to assess whether child development is associated with pregnancy planning.

So a team of UK researchers set out to investigate how pregnancy planning, time to conception, and infertility treatment influence a child's cognitive development at three and five years old.

They analysed data from approximately 12,000 children from the Millennium Cohort Study, a large UK study of families and infants born in 2000-2. Parents who took part were interviewed when their child was nine months old and then revisited when the child was three and five years old.

Mothers reported whether the pregnancy was planned, their feelings when first pregnant, time to conception, and details of any infertility treatment.

Each child's verbal, non-verbal and spatial abilities were tested at age three and five using the British Ability Scales.

Initial analyses showed that children born after an unplanned pregnancy were four to five months behind planned children in verbal abilities, while children born after assisted reproduction were three to four months ahead.

However, these differences all but disappeared when the researchers took into account the socioeconomic circumstances of each child.

The authors conclude: "These differences are almost entirely explained by socioeconomic factors, providing further evidence of the influence of socioeconomic inequalities on the lives of children in the UK. To help children achieve their full potential, policy makers should continue to target social inequalities."