- Embryo vs. Fetus: Differences between Stages Week by Week Center
- Ovulation & Fertility Slideshow Pictures
- Early Pregnancy Symptoms Quiz
- Stages of Pregnancy Slideshow Pictures
- Find a local Doctor in your town
Embryo vs. fetus week by week
- The terms embryo and fetus both refer to the developing baby inside the mother’s womb (uterus).
- The distinction between embryo and fetus is made based on gestational age.
- An embryo is the early stage of human development in which organs are critical body structures are formed.
- An embryo is termed a fetus beginning in the 11th week of pregnancy, which is the 9th week of development after fertilization of the egg.
- A zygote is a single-celled organism resulting from a fertilized egg. The zygote divides to become a ball of cells that eventually implants in the wall of the uterus.
- This ball of cells, known as a blastocyst, develops into the embryo and placenta.
- Doctors date pregnancy from the first day of the last menstrual period.
What is an embryo?
Doctors define pregnancy according to the date of a woman’s last menstrual period.
- The first two weeks of pregnancy are counted as the time prior to ovulation, in which the body is preparing to release an egg.
- Week #3 begins with release of an egg, or ovulation. If the egg is fertilized by a sperm cell, it is known as a zygote. The zygote divides and becomes a collection of cells known as a blastocyst.
- In week #4 of pregnancy, the blastocyst implants in the wall of the uterus and develops into the placenta and embryo. The blastocyst is considered an embryo at the point when the amniotic sac develops (by about day 10 to 12 after fertilization, or at the start of week #5 of pregnancy).
- An embryo represents the early stage of human development, roughly corresponding to the 5th-10th weeks of pregnancy.
What is a fetus?
After the embryonic period has ended at the end of the 10th week of pregnancy, the embryo is now considered a fetus. A fetus is a developing baby beginning in the 11th week of pregnancy.
The developing embryo: Week #4 to Week #11
The embryonic period of development is the stage in which most organs are formed. Organs begin to form, and the embryo elongates and starts to assume a human-like shape. The heart and main blood vessels are formed, and the heart starts beating by the 6th week. The primitive brain and spinal cord (neural tube) also begin to form.
By 12 weeks of pregnancy almost all of the baby’s organs are formed, including the arms and legs. The brain and spinal cord, however, continue to develop throughout pregnancy. The baby is about 2 inches long at the end of the embryonic period.
Most birth defects occur during the embryonic period, the critical time when organs are forming. The embryonic period is the time of greatest susceptibility to the negative effects of drugs, radiation, and viral infections.
Fetal period: week #12 to week #40
The fetal period is a time of growth of the developing baby. The organs and structures formed in the embryonic period continue to grow and develop.
The second trimester begins in the 13th week. By about 14 weeks of pregnancy, the gender of the fetus can be identified. Women can begin to feel movement of the fetus somewhere between the 16th and 20th weeks of pregnancy. The baby grows to about 2 pounds during the second trimester.In the third trimester, starting in the 27th week, the baby assumes the size and characteristics of a newborn and prepares for birth. The fetus will open its eyes and breathe in the amniotic fluid.
Your first prenatal visit with your doctor or midwife
You should set up an appointment with your doctor or midwife as soon as you have a positive pregnancy test result. At the initial visit, your doctor or midwife will
- Discuss your medical history and any effect this may have on your pregnancy.
- Estimate your due date.
- Perform a physical examination.
- Order lab work to look for any infections and to determine your blood type, immunity against certain infections, and your red blood cell count
- Discuss any medications you are taking, and whether you will need to alter these during pregnancy and discuss the need for vitamins or supplements during pregnancy
- Discuss expected weight gain, activity level, and nutrition for a healthy pregnancy
- Provide contact information to call in case you have any questions, or are worried that something is wrong
- Answer any questions you may have
- Set up your next appointment and discuss how often you should visit your doctor or midwife.
Which stage has the most risk of miscarriage?
The greatest risks of miscarriage are in the very early stages of pregnancy. An estimated 25% or more of pregnancies end in the very early stages, many before a woman even knows that she is pregnant or has missed a menstrual period. Most other miscarriages happen in the first 12 weeks of pregnancy when the embryo is developing.
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Brown, HL., MD. "Stages of Development of the Fetus."Merck Manual. Consumer Version.
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Pregnancy Symptoms QuizWhat are early pregnancy symptoms? In some women, symptoms range from a missed period to feeling lightheaded. Others may experience typical "morning sickness" and food cravings. Could you be pregnant? Take the quiz!
An ectopic pregnancy is a pregnancy located outside the inner lining of the uterus. The majority of ectopic pregnancies occur in the Fallopian tube. Signs and symptoms of an ectopic pregnancy may include:
- Abdominal pain
- Lack of menstrual period (amenorrhea)
- Vaginal bleeding
- Low blood pressure
Treatment options for an ectopic pregnancy include observation, medication, or surgery.
Heartburn and Pregnancy
Heartburn during pregnancy is quite common. During pregnancy the lower esophageal sphincter muscle becomes weakened , which likely occurs due to the effect of the high levels of the hormones estrogen and progesterone during pregnancy. Fortunately, this resolves after pregnancy. Management of heartburn during pregnancy are generally involves lifestyle changes and avoiding foods that promote heartburn, for example, don't smoke, avoid tight clothing, eat small, frequent meals, chew gum, or sip liquids.
The effect of heartburn medications on the fetus is unknown, so it is best to check with your OB/GYN if you feel you need medication to treat heartburn.
Ovulation & FertilityBoost fertility and increase your chances to conceive. Learn about ovulation calendars, diet, aging and other factors that can affect pregnancy.
Signs and symptoms of pregnancy vary by stage (trimester). The earliest pregnancy symptom is typically a missed period, but others include
breast swelling and tenderness,
- nausea and sometimes vomiting,
- fatigue, and
Second trimester symptoms include
- weight gain,
- itching, and
- possible stretch marks.
Third trimester symptoms are
- additional weight gain,
- swelling of the ankles,
- fingers, and face,
- breast tenderness, and
- trouble sleeping.
Eating a healthy diet, getting a moderate amount of exercise, also are recommended for a healthy pregnancy. Information about the week by week growth of your baby in the womb are provided.
Pregnancy can bring challenges like
- weight gain,
- stretch marks,
- varicose veins,
- problems sleeping, and
- wondering if it is safe to have sex while pregnant.
Learn how to manage and move through these challenges during pregnancy.
Pregnancy Drug DangersTaking prescription medications or over-the-counter drugs or supplements should be discussed with your doctor. There are some medications that have been found to cause no problems in pregnancy, however, medications such as Accutane for acne, should never be taken during pregnancy.
Pregnancy Myths QuizBeing pregnant is a delicate time for both mother and baby. Take this quiz to separate the myths and facts about being pregnant, and learn the truth behind healthy pregnancies!
Pregnancy Planning (Preparing for Pregnancy)
Pregnancy planning is an important step in preparation for starting or expanding a family. Planning for a pregnancy includes:
- Taking prenatal vitamins
- Eating healthy for you and your baby
- Disease prevention (for both parents and baby) to prevent birth defects and infections
- Avoiding certain medications that may be harmful to your baby
- How much weight gain is healthy
- Exercise safety and pregnancy
- Travel during pregnancy
Pregnancy Symptoms Am I PregnantPregnancy symptoms can vary from woman to woman, and not all women experience the same symptoms. When women do experience pregnancy symptoms they may include symptoms include missed menstrual period, mood changes, headaches, lower back pain, fatigue, nausea, breast tenderness, and heartburn. Signs and symptoms in late pregnancy include leg swelling and shortness of breath. Options for relief of pregnancy symptoms include exercise, diet, and other lifestyle changes.
Pregnancy: Your Guide to Eating Right
When a woman is pregnant she needs more vitamins, minerals, and other foods in her diet to stay healthy and deliver a healthy baby. A healthy pregnancy diet menu plan should consist of lots of fruits, vegetables, lean meats (unless you are vegan or vegetarian), and dairy. Examples of healthy pregnancy diet meal plans include:
- Holistic pregnancy diet
- Vegan or vegetarian diet
- Low-carb diets
Begin your healthy eating plan around three months before you begin trying to conceive, and follow the same eating plan until after you have stopped breastfeeding. If you are overweight or obese, being pregnant is not the right time to try to lose weight. Discuss your options with your health-care professional.
Sex Life After BabyLearn how your sex life changes after having a baby. Explore tips on how to regain sexual desire and strengthen your relationship after pregnancy.
Sexually Transmitted Diseases and Pregnancy (STDs)When you are pregnant, many sexually transmitted diseases (STDs) can be especially harmful to you and your baby. These STDs include herpes, HIV/AIDS, genital warts (HPV), hepatitis B, chlamydia, syphilis, gonorrhea, and trichomoniasis. Symptoms include bumps, sores, warts, swelling, itching, or redness in the genital region. Treatment of STDs while pregnant depends on how far along you are in the pregnancy and the progression of the infection.
Stages of PregnancySee pictures on the various stages of pregnancy. See and learn what changes a woman's body goes through and view fetal images of how her baby grows during the 1st, 2nd and 3rd trimesters.
Trying to Conceive
Trying to get conceive, or become pregnant can be challenging, frustrating, and an emotional rollercoaster for some couples. A couple can chart their progress, which may ultimately lead to a successful healthy pregnancy, or, when necessary, lead to discussions with a fertility specialist. If you're a woman, be aware of your menstrual cycle, and you can track when you are fertile during the month using the:
- Basal body temperature method
- Calendar method
- Ovulation method (cervical mucus)
About 10% of women in the US have problems getting pregnant, or carrying a pregnancy full term. Both men and women can have fertility problems. In fact, men and women each contribute about 1/3 when it comes to fertility problems. The other 1/3 are caused by a mixture of problems with both men and women or other problems that aren't identifiable.
Tubal Pregnancy PictureA pregnancy that is not in the usual place within the uterus but is located in the Fallopian tube. See a picture of Tubal Pregnancy and learn more about the health topic.