Human gestational development

Overview

The exact manner in which unborn human beings develop while in the womb is of great significance in the ongoing debate over abortion.

Timeline

• First trimester (months 1-3)
• T = 0 Fertilization: sperm enters egg, and egg begins to divide.
• T = week 8: beginning of the fetal stage:
  • Fetus is typically about 30 mm (1.2 inches) in length from crown to rump, and weighs about 8 grams
  • Breathing-like movement of the fetus is necessary for stimulation of lung development, rather than for obtaining oxygen
  • The heart is beating.
  • Fetus cannot survive on its own
  • Current understanding is that fetuses are not capable of feeling pain at this point, though it's not clear how this is determined (especially since we don't yet understand how pain is "understood" by the brain, i.e. what makes it different from any other sensation). See wikipedia:Fetal pain.
• T = week 11: first measurable signs of EEG movement occur, i.e. the brain is known to be operating at some level at this point. It may be operating before this and simply undetectable with current instruments. On the other hand, it isn't known what the brain's capabilities are (including whether it can feel any kind of pain) at this point.
• Second trimester (months 4-6) begins at approximately week 13-14 (query: is there a legal definition?)
• T = weeks 15-24: The nervous system develops enough to control some body functions during this time. Multiparous women may feel some movement at 16 weeks, while others typically feel the first movements at 18-19 weeks.
• Third trimester (months 7-9) begins at approximately week 25-26
• T = weeks 25-37: The brain forms thalamic connections, which mediate sensory input, during this time.
• T = week 38: birth typically happens at this time

"Trimester" plays a significant part in the abortion laws of many countries; see wikipedia:Abortion law.

Links

Reference

• Wikipedia:
  • Pregnancy
  • Embryo
• MedLine Plus Medical Encyclopedia: Fetal development
• The Biblically-Correct Conservapedia doesn't seem to have much info on this
• dKosopedia and SourceWatch deal mainly with issues, not the biological details