Beginning of second trimester is marked with the onset of the fourth month. At 13-14 weeks, the foetus measures about 7,5 cm (3 inches). At this time, the foetus’ sex can be determined by an ultrasound. Growth of small hairs can be seen and the roof of the mouth also begins to form. The foetus is about 11,5 cm (4.5 inches)long and weighs around 85 gram (3 ounces)during the 15th week and in female foetuses, the eggs begins to form in the ovaries.