Maternal-Newborn and Pediatric Nursing · Chapter 2
The First Ten Days and the Date on the Chart
Everything in this chapter is anchored to a day. Drag the conceptus along the tube and watch fertilization, cleavage, blastocyst and implantation happen on schedule, then date a real pregnancy with Naegele rule and see why gestational age and post-fertilization age never agree. Finish by setting the day a monozygotic pair divided — because that single day decides how many membranes they share and therefore how dangerous the pregnancy is.
Set the clock
Day 0
Day 0 is the moment of fertilization in the ampulla. Obstetric charting does not count from here — it counts from the first day of the last menstrual period, about two weeks earlier.
The fertile window
The secondary oocyte can be fertilized for roughly 12 to 24 hours after ovulation. Sperm survive in the female tract for up to 5 days. Add them and the fertile window is about six days — the five days before ovulation plus the day of ovulation itself. Teach that window and you have taught both contraception and conception.
Naegele rule assumes a regular twenty-eight-day cycle with ovulation on day fourteen. Say that out loud before you write the date in the notes.
Day 2
Only meaningful for a monozygotic pair. Tick the box above and the slider stops mattering — which is itself the teaching point.
Why chorionicity is the whole question
Shared circulation is the danger. Two placentas cannot transfuse each other. One shared placenta can, and one shared sac adds cord entanglement on top. Monozygotic twinning occurs at a fairly constant rate of about 1 in 250 births worldwide; dizygotic rates rise with maternal age, with a family history on the maternal side, and markedly with ovulation induction and assisted reproduction.
FertilizationAmpulla of the fallopian tube, within 24 hours of ovulation