The embryonic stage lasts for eight weeks after fertilization occurs (2). The placenta should normally last for the entire pregnancy and will be either pushed out of the uterus with a vaginal birth or removed during a cesarean section when the fetus is born. The placenta also makes hormones that maintain the pregnancy, influences changes in the body, and provides what the fetus needs to grow and develop (3). The placenta is an important organ formed inside the uterus during pregnancy that has several functions, such as bringing nutrients and oxygen to the embryo or fetus and carrying wastes and carbon dioxide away through the umbilical cord (2). The placenta is an organ specially formed from the blastocyst cell layer called the trophectoderm (3). The embryo (and later the fetus) is reliant on the pregnant person’s blood (which carry oxygen and nutrients) through the placenta. By the end of the 3rd week of pregnancy (when counting from the last period), the embryo is receiving nutrients from the pregnant person’s blood supply (2). It occurs 5-6 days after ovulation and closes 3-4 days later (3). Successful pregnancies typically burrow or implant during the implantation window, which is the receptive phase of the endometrium. The embryo is now called a blastocyst (2).Ībout six days after fertilization, the blastocyst typically attaches to the endometrium (uterine lining) and over the next few days burrows through the endometrium so that it can take nutrients from its surroundings (2). About four days after fertilization the morula nears the uterine cavity (inside of the uterus) it develops a fluid pocket called a blastocele, forming a pocket of fluid surrounded by cells (3). Once the embryo contains 12 to 16 cells, it is called a morula (2). The zygote repeatedly divides into smaller embryonic cells. The DNA from these two cells combine, forming a zygote (2). In this article, we will be using gestational age based on the time from the last menstrual period meaning you are two weeks pregnant the day you become pregnant, unless otherwise noted.įertilization occurs when a sperm cell enters a mature oocyte (egg cell) (2). This creates a two-week(ish) discrepancy between the actual age of an embryo or fetus (which begins with fertilization) and how we estimate it based on someone’s last period. Of course, this assumption may be inaccurate because there is a range of typical menstrual cycle lengths and the day of ovulation can fluctuate cycle-to-cycle, even for the same person. The timing of ovulation during the menstrual cycle can vary, but the clinical method of determining gestational age assumes that it occurs on the 14th day of a 28-day cycle (1). Fertilization usually occurs within 12 hours after ovulation (2). The exact date of fertilization is typically harder to identify (except in cases of assisted reproductive technology, like in vitro fertilization or IVF). For embryologists (people who study the development of embryos), gestational age is based on the timing of fertilization (2). In a clinical setting, like when you see your healthcare provider, gestational age is estimated from the first day of the last menstrual period (LMP) because this is typically an easy date to pinpoint for the pregnant person (1, 2). When someone says they are 15 weeks pregnant, for example, this is the gestational age of their fetus. The gestational age is the age (usually in weeks) of the embryo or fetus. A better understanding of embryonic and fetal development can expand our word choices.įirst, a note about how the timing of these different stages of pregnancy are measured. It may not be common to hear a pregnant person speak about their embryo or fetus in those terms, but we can all choose to use the words we are most comfortable with. The fetus becomes a neonate or newborn at birth. As pregnancy progresses the embryo becomes a fetus. When egg and sperm meet, a zygote is formed and quickly begins dividing to become an embryo. While you likely hear people talk about the “baby” when someone is pregnant, there are specific terms that describe the different stages of pregnancy. Unfortunately, language has become part of the fight over access to abortion The language we use to describe pregnancy and the developing embryo or fetus is important. The embryonic stage begins with fertilization and lasts for eight weeksįrom the 10th week of pregnancy (if you’re counting from the start of the last period) until birth is the fetal stageĪ rapid and complex transition happens at birth, from dependent fetus to independent newborn
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |