Her twin sister was also a small baby, weighing 563 grams (1 lb 3.9 oz) at birth. During pregnancy their mother had suffered from pre-eclampsia, which causes dangerously high blood pressure putting the baby into distress and requiring birth by caesarean section. The larger twin left the hospital at the end of December, while the smaller remained there until 10 February 2005 by which time her weight had increased to 1.18 kg (2.6 lb).[155] Generally healthy, the twins had to undergo laser eye surgery to correct vision problems, a common occurrence among premature babies.