During What Paer of Devolpment Is the Baby a Fetus

This fact sheet is about the critical periods of development and types of nascence defects that tin can outcome from exposures at different stages of pregnancy. This information should not take the place of medical care and advice from your healthcare provider.

What are critical periods of development?

In pregnancy, each part of the infant's body forms at a specific time. During these times, the body can exist very sensitive to damage caused by some medications, alcohol, or other harmful exposures. This specific fourth dimension is called the "critical menstruation of development" for that body part.

Does the adventure for different types of nascence defects change throughout pregnancy?

Every pregnancy starts out with a 3-5% risk of having a birth defect. This is called the background risk. If an exposure can increase the chance for birth defects, the chance depends on what trunk part is developing at the time of exposure. Once a body office has formed, it is no longer at risk to develop major birth defects. Some exposures could still affect a torso part's growth and/or part.

The chart in this fact sheet shows the disquisitional periods of development for different parts of the body. The chart starts from the time of conception when the egg and sperm bring together. The weeks listed on the chart are the "embryonic age" or "fetal age" of a pregnancy. Notation that this is different from a common way of dating a pregnancy called "gestational age." Gestational age begins with the start twenty-four hour period of a person's last menstrual period. This day is commonly about ii weeks before a baby is conceived. This means that y'all can modify gestational age to embryonic/fetal age by subtracting ii weeks. For case, 12 gestational weeks (since the starting time twenty-four hours of your last catamenia) is the same every bit 10 fetal weeks (since the showtime day of conception).

The solid confined on the chart evidence when each function is virtually sensitive to harmful exposures and at risk for major birth defects. Nascency defects are typically classified equally "major" if they cause significant medical bug and need surgery or other treatment. Heart defects, spina bifida, and clubfeet are examples of major birth defects.

The striped bars testify periods when the trunk parts are even so at risk to develop minor nativity defects and functional defects. "Modest" birth defects by themselves do not cause significant medical issues and usually do non require treatment or surgery. Small birth defects can also be variations of typical development. Wide-set eyes and large ears are examples of minor nascency defects.

Both major and small-scale birth defects are physical or structural changes. However, "functional defects" modify how a part of the body works without changing its physical structure. Intellectual inability and hearing loss are both examples of functional defects.

The chart also shows the location of the well-nigh common nascence defects that can occur during each week. In general, major defects of the body and internal organs are more likely to occur betwixt iii to 12 embryo / fetal weeks. This is the aforementioned as 5 to fourteen gestational weeks (weeks since the outset day of your last period). This is also referred to as the first trimester. Small defects and functional defects including those affecting the brain are as well able to occur later in pregnancy.

*Adjusted from Moore 1993, and the National Arrangement of Fetal Alcohol Syndrome (NOFAS) 2009.

What is the greatest adventure from a harmful exposure during very early pregnancy?

Harmful exposures during very early on pregnancy accept the greatest risk of causing miscarriage. A fertilized egg divides and attaches to the within of the uterus during the first two weeks of embryo development. Very harmful exposures during this catamenia (starting time iv weeks after the outset mean solar day of your final catamenia) may interfere with the attachment of the embryo to the uterus. Harmful exposures during this fourth dimension can also damage most or all of the cells of the growing embryo. Problems with uterine attachment and severe prison cell damage can both event in a miscarriage. Sometimes this miscarriage is earlier a person fifty-fifty realizes that they are pregnant.

Less severe exposures during this time may just impairment a few of the embryo'due south cells. The cells of the embryo have a greater ability to recover at this early on stage than they practise afterward in pregnancy. If an private does non have a miscarriage, it is expected that the exposures during this fourth dimension are not likely to cause a birth defect.

The first 4 weeks of gestation are called the "all or none period." "All" refers to loftier exposures dissentious all of the embryo's cells. This damage can cause early on miscarriage. "None" refers to exposures that are non high enough to accept a pregnant effect on the pregnancy. The rule of the "all or none period" tin can be used to make up one's mind the chance of many dissimilar types of exposures. All the same, there are some important exceptions to this dominion. Please contact MotherToBaby to discuss your specific exposure with our experts.

What are the greatest risks from harmful exposures during the beginning trimester of pregnancy?

The first trimester of pregnancy is defined every bit up to the 14th week of pregnancy (13 weeks and half dozen days) counting since the first day of your last menstrual period. Harmful exposures during the first trimester have the greatest chance of causing major nascence defects. This is because many important developmental changes take place during this time. The major structures of the trunk form in the first trimester. These include the spine, head, arms and legs. The baby'southward organs also begin to develop. Some examples of these organs are the heart, stomach and lungs. While the heart and tummy completely class during the first trimester, the lungs continue to develop past the first trimester.

What are the greatest risks from harmful exposures during the second and tertiary trimesters of pregnancy?

Harmful exposures during the 2nd and third trimesters can cause growth bug and small nascence defects. Growth is an of import part of the second and third trimester. The structures and organs that developed during the first trimester abound larger. Babies with growth bug may be much smaller or much larger than average. This size difference can put babies at risk for certain wellness bug.

Harmful exposures during the second and third trimesters can also cause functional defects like learning problems. The brain is office of the key nervous system and it develops during the entire pregnancy. Major, structural brain development lasts until nigh 16 fetal weeks (xviii gestational weeks). However, the encephalon continues to develop for the rest of the pregnancy, afterwards birth and through young adulthood.

While usually less well studied, some exposures in the second or tertiary trimester might crusade other pregnancy complications, such as preterm delivery (delivery before 37 weeks gestation) or low levels of amniotic fluid (the fluid that surrounds the developing baby in the uterus).

The use of sure medications and substances at the terminate of pregnancy tin crusade withdrawal in some newborns. You should always tell your healthcare provider almost all of the medications, supplements and/or other substances that you take.

Does this mean that an exposure might be harmful at sure times during pregnancy but not at other times?

Yeah. Imagine your healthcare provider gives yous a new medication to have during your 3rd trimester. We will call this "Medication A." Y'all read that Medication A increases the chance for center defects. This means that babies may take a higher chance for major middle defects if they are exposed to this medication during the middle's critical menstruum of development. The heart'southward disquisitional period of development is from 3 to six embryonic weeks (5 to viii gestational weeks). This means that using this medication in the third trimester cannot cause a major heart defect. Always talk to your healthcare provider before making any changes to how y'all have your medication.

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OTIS/MotherToBaby recognizes that non all people identify as "men" or "women." When using the term "mother," we mean the source of the egg and/or uterus and by "father," we mean the source of the sperm, regardless of the person's gender identity.

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Source: https://mothertobaby.org/fact-sheets/critical-periods-development/