A timeline of the odds for survival for fertilized eggs and fetuses

  • 266 days before birth, all we have is a fertilized egg. (~33% chance of living birth).
    The odds are calculated using data from in-vitro fertilization, and the next stage is 66%.
    In in-vitro, some 50% of the eggs cannot fix to the uterine wall
  • 262 days before birth, the egg has implanted (~66% chance of living birth)
    After implantation, there is still a decent chance that the embryo will be aborted (and maybe the woman will not even know that she was pregnant).
    Half of the embryos that die from here on will die because of chromosome abnormalities.
  • 241 days before birth (~88%)
  • 178 days before birth, entering the second trimester (~97%) At this stage, problems are more likely to stem from the mother, not the fetus’ genome. Problems with the cervix, the uterus or the placenta are (some ?) likely causes of death.
  • 89 days before birth, entering the third trimester (~99%) At this stage, doctors will consider the fetus a patient, and treat it if needed.

Baby’s Development Month by Month

At the earliest stage, the new person is referred to as a zygote and is no larger than a single grain of sand.

.. A function called implantation happens from five to nine days after fertilization.

.. Once he/she has implanted, your baby is called a blastocyst and is about 0.1 – 0.2 mm in diameter.

.. Between weeks three and four (18 to 25 days after fertilization) the developing baby’s heart begins to beat. Arm and leg buds form. The face – eyes, ears, nose and mouth – begin to take form.

.. Month Two  .. Your baby now is only about one inch long and weighs no more than one whole peanut.

.. The lining of the placenta begins to develop but does not take over the production of hormones until about week 12. Brain waves are detected.

.. When you see your baby through ultrasound at week six, you’d be amazed by how much he or she has already developed.

.. the end of month two, your baby receives a new technical name to describe his/her development: fetus

.. All organs are present – and most are functioning – although some need more time to develop. The irises of the eyes develop, fingernails are visible and your baby can curl his/her fingers around an object. He or she also hiccups, has taste buds on the tongue and tooth buds in the gums.

.. Month Three
Your baby can smile, make funny faces. She/he can practice “breathing” the amniotic fluid in/out of the lungs, all 20 teeth are formed and waiting to develop. Your baby is now approximately one ounce in weight

.. At 15 weeks, loud sounds may actually cause baby to startle. Some moms and dads find that quiet music played near mom’s tummy will cause baby to relax and calm down.

.. Month Four
Your baby is now about eight inches tall from head to toe.

Which fertilized eggs will become healthy human fetuses? Researchers predict with 93% accuracy

Because the parameters measured by the researchers in this study occur before any embryonic genes are expressed, the results indicate that embryos are likely predestined for survival or death before even the first cell division.

.. Despite their best efforts, though, they have only about a 35 percent success rate. As a result, most women elect to transfer two or more embryos to increase the chance of a live birth.

.. the embryos at first express only genes from the maternally derived egg. By roughly the third day (the eight-cell stage) they begin to express genes specific to embryonic development

..  The researchers found embryos in which some cells were dividing on schedule while others were seemingly stuck, or paused.

..  embryos in which individual cells varied significantly in their cell-division schedules or gene-expression profiles were less likely to become successful blastocysts.

.. Cells that fail to execute some part of this delicate process get out of sync with their neighbors and jeopardize the life of the embryo.

.. “In mice, about 80 to 90 percent of embryos develop to the blastocyst stage. In humans, it’s about 30 percent,” said Reijo Pera.

.. “In addition, about one in 100 mouse embryos are chromosomally abnormal, versus about seven out of 10 human embryos.