# What week starts 3rd trimester of pregnancy?

Often expectant mothers, when calculating the period of pregnancy there is confusion, especially when it comes to trimesters. This time period is commonly understood as 3 calendar months. However, most often the very length of gestation is considered in the so-called obstetric months. Latest from the calendar differ in that lasted exactly 4 weeks. Let’s take a closer look at the features of the calculation period and will give the answer to the question as to what week starts the 3rd trimester of gestation that precedes birth.

How long is the entire period of gestation?

Before you call the period when starts the 3rd trimester of pregnancy, consider the whole process of gestation in weeks.

So, according to obstetric term, all the normal pregnancy lasts 280 days. Thus the starting point for the commencement of this time period is the last day of the last menstrual period. For greater convenience and correctness of counting, obstetricians usually divide the pregnancy into trimesters.

The first trimester, or as it is called early fetal, begins from conception and lasts until the 13th week of pregnancy. At this time there is implantation of the ovum in the endometrium that actually tells about the beginning of pregnancy. The period is characterized primarily by the formation of axial organs and systems of the future baby.

Second trimester starts from 14 weeks and ends on 27. It is characterized by the maturation and growth of already formed organs.

If you talk about how many weeks starts the 3rd trimester, it is 28 week of gestation. This time period is characterized by significant growth of the already formed child. It ends with birth, which normally are observed at 40 weeks of gestational process.

What changes occur in the 3 trimester of pregnancy in the mother and baby?

Having dealt with when, or rather, how many weeks starts the 3rd trimester of pregnancy, will give a brief characterization of this time period.

Every day the baby grows, which leads to an increase of the height of standing of bottom of uterus. For example, at 28 weeks this option is 29-30 cm, and already on 36 week – 37 cm that is why the expectant mother quite often it becomes difficult to breathe, develops shortness of breath, worsening after physical exertion, such as after climbing stairs.

Also we can not say about training fights, which at this time occur more often (can be recorded up to 10 times per day). Thus the woman must know exactly how them to distinguish from generic because there is always the possibility of premature birth.

As for the kid, that at this period all systems and organs are formed and actively functioning. With the exception, perhaps, is only the respiratory system that begins to work with the advent of the baby born.

The lungs before birth are not in the expanded state. For this to happen, starting with 20 weeks begins to synthesize a substance such as surfactant, which prevents the decay of the alveoli. It should be noted that Matures this system only to the 36 week of gestation. Therefore, the appearance of the baby born earlier than this period may be accompanied by disruption of the respiratory system.

Thus, as can be seen from article 3 trimester of pregnancy is not less important than the 2 previous. At this time, the expectant mother should be actively preparing for her birth process and strictly follow the instructions of the doctor. If the woman noticed something strange, there was pain in the lower abdomen, — it is necessary to inform the doctor.