Ah alam ko kung bakit ka confused! So kung April 19 ang due date, that means conception was around mid-July of the previous year, pregnancy is about 40 weeks, kaya basically 9 months backwards from due date. So kung December ang last period, baby was formed around mid-January, pero the pregnancy itself "started" counting from that last period in December, kung gets mo? That's why doctors count from LMP (last menstrual period), not from actual conception, medically mas convenient kaya sometimes nakaka-confuse talaga!