A new meta-analysis looking at the effect of abstinence-only sex education found that it may have had the opposite effect of the one intended.

Since the mid-1990s, over $2 billion has been spent on abstinence-only sex education programs in the US. Trump has indicated that he would like to increase spending in this area, at the expense of sex education that informs teens about contraception and protective sex.

But does abstinence-only sex education actually work?

The new study looked at the adolescent birth rate (live births for girls aged between 15 and 19 years old) per 1,000 between 1998 and 2016, as provided by the Centers for Disease Control and Prevention (CDC), as well as spending focused on abstinence-only and comprehensive sex education across the USA.

The study, published in the American Journal of Public Health, found that abstinence-only education had had no overall effect on the birth rate amongst teens, whilst in conservative states that pushed this education there had been a perverse effect:

Abstinence-only education actually increased the birthrate in conservative states.

The authors found that an increase in spending on abstinence-only or "wait until marriage" education had no overall effect on teenage birth rates throughout the whole USA, but increased births in politically-conservative states.

"Specifically, we estimated that conservative states received $692 million in federal abstinence funding between 1998 and 2016," the authors write in the study. "In 2008 alone, conservative states received more than $71 million in abstinence funding, which amounts to $4.52 per pupil."

"With an average effect of raising births by 0.2 (0.30 + –0.06) per 1,000, we estimate that the change in the birthrate from this single year of abstinence funding amounted to a change in the birthrate of 1.08 per 1,000, or 1,080 additional births, to adolescents than would have otherwise been the case."

Spending money on abstinence-only education in order to prevent teen pregnancies actually lead to a notable increase in teenagers giving birth.

The new study has added to several other studies that have repeatedly found abstinence-only education to be ineffective. As well as leading to increases in births to teenage mothers in conservative states, it also doesn't lead to a decrease in young people having sex, or avoid unwanted pregnancies and sexually transmitted disease.

Who'd have thought it, the most effective way of stopping teenagers from getting pregnant is to teach them about contraception.