Twins With A Twist

What do you call siblings born on the same day? Twins? Triplets? Well, this is not always the case,

- Camilla Rankin

FALLING PREGNANT WITH a second baby while you’re still pregnant with the first? Sounds impossible, or like the tacky storyline of a terrible soap opera, but it can, and does, happen.

TWO TIMES, A BABY…OR TWO

Falling pregnant again while already pregnant is an extremely rare and unusual phenomenon, and depending on when the second egg was released, is known as superfoetation or superfecundity – where ‘fecund’ means highly fertile or capable of producing an abundance of offspring.

Superfecundity occurs when two eggs are released in one cycle and are fertilised five to seven days apart, after having sex at least twice during that time. These babies will develop like twins in two separate amniotic sacs, but can be measurably different sizes. Superfoetation, however, is much rarer – in fact the jury is still out as to whether it can happen at all – but is when one egg is released and fertilised during one cycle, and then another egg is released and fertilised in a subsequent cycle. In both cases the babies will develop and grow according to their gestational age and are often mistaken for twins, where one is just much smaller than the other.

True twins are conceived by either one fertilised egg splitting in two (identical twins), or when two eggs are released and fertilised within five days of sex (fraternal or non-identical twins). Male sperm can survive in the female body for up to five days, so superfecundity refers to cases where the second egg is fertilised outside of that five-day window period.

IN THE NORMAL COURSE OF EVENTS