Common Clinical Words


Written by : Dr.M.D.Mazumdar, MD

Certain words are used repeatedly while discussing issues related to pregnancy. A brief description of the meaning of each word is given on this page.

Zygote

The single cell that results from the fertilization of the ovum by the sperm.

Embryo

When the single celled zygote starts to divide, it is called an embryo. The term embryo is used until the end of the eighth week of pregnancy. At this stage, it is 3.5 cm in length and about 2gms in weight.

Fetus

The word fetus is used to describe the developing baby from the end of the eighth week till the last week of pregnancy. From the eighth week onwards, the foetus floats freely in the liquor amnii connected to the uterus only by the umbilical cord. It is able to move and swim in the liquor and begins to show features of a human being, with development of eyes, ears and limbs.

Last Menstrual Period (LMP)

This is the date of the first day of the last menstrual period that a woman has had before she became pregnant.

The Expected Date of Delivery (EDD)

Also called the Expected Due Date, this is the date at which the baby is expected to be delivered. This is calculated from the first day of the Last Menstrual Period (LMP). Two methods are usually employed to calculate the EDD:

  • Nine months are calculated from the first day of the LMP and seven days are added to the answer. For example, if the LMP is 3rd March, the EDD will be 3rd December plus seven days, that is 10th December.

  • Three months are counted backwards from the first day of the LMP and seven days added to the answer. For example, if the LMP is 3rd March, three months counted backwards will take us to the 3rd of December. Seven days added to it will be 10th December.

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But these methods are accurate only if the menstrual cycle is regular and 28 +/- 2 days. If cycle length is longer, say 32 days then the extra days beyond 28 days, i.e 4 days have to be added to the EDD.

So a woman whose LMP was on the 3rd of March, but whose cycle length is 32 days will have her EDD on the 9 months +7days +4 days = 3rd December +7days+4days= 14th December. Similarly if the cycle length is less, the same number of days have to be subtracted from the calculation. Only about 10% of women deliver on the EDD.

Most women deliver within the first week of the EDD. Delivery between three weeks before and two weeks after the EDD is considered normal.

Trimester

The entire duration of pregnancy is divided into three parts for the purposes of management of pregnancy. Each division, called a 'trimester' is approximately 13 weeks long :

    1st Trimester - from the beginning of pregnancy till the end of the thirteenth week.

    2nd Trimester - from the end of the 13th week to the end of the 26th week.

    3rd Trimester - from the end of the 26th week to the end of the 40th week.

Lie

This is the relation of the fetal spine with that of the maternal spine.
  • Vertical Lie If the fetal spine is more or less parallel to that of the maternal, the lie is said to be 'Vertical'. In most babies, the lie is vertical.

  • Transverse Lie If the foetal spine is at a right angle to the maternal spine, the lie is 'Transverse'. This presentaiton is not very common.

  • Oblique Lie If the foetal spine is oblique across the maternal spine, the lie is 'Oblique'. This is also a common lie. At the time of labour, when the uterus starts to contract, this lie quite often changes to Vertical.

  • Unstable Lie If the lie of the foetus is found to change very often, it is called an 'Unstable lie'.

Presentation

Presentation indicates the part of the foetal body that presents at the cervix at the time of labour. ABout 95% of all babies have a cephalic (meaning 'head') presentation.

A. Cephalic Presentation There are three types of cephalic presentation.

  • Vertex Presentation The vertex is a quadrangular area on the top of the head surrounded by the bony sutures of the skull bones.

  • Brow Presentation The brow is defined as the area bounded above by the sutures on top of the forehead and below by the root of the nose and supra orbital ridges.

  • Face Presentation This is the area bounded on one side by the root of the nose and the supra-orbital ridges and on the other side by the junction between the floor of the mouth and the neck.

B. Breech Presentation This is presentation in which the baby's buttocks with lower limbs present at the cervix during labor.

B. Shoulder Presentation This presentaiton is seen together with transverse lie and is not very common.

Abortion

Although the word 'miscarriage' is freely used to describe the loss of a foetus in early weeks of pregnancy, the correct medical term is 'Abortion'. An abortion, whether spontaneous or induced, is said to have occurred when a foetus less than 500 gm in weight or less than 22 weeks of gestational age is expelled from the body.

Ovulation, Fertilization and Implantation

Ovulation, fertilization and implantation are important steps to how a pregnancy occurs .

An ovum is released from the ovary approximately 14 days (12 to 16 days) after the last menstrual period. Fertilization occurs when the male sperm meets the female ovum and fuses with it to form the zygote. It usually occurs in the outer part of the fallopian tube.

The single celled zygote starts to divides in about 12 hours into 2 cells. It continues to divide into more cells as it is propelled towards the uterus by the ciliary cells lining the inner wall of the tube as well as by the movement of the tube itself. By the time it reaches the uterus it is a cluster of sixteen cells called a 'morula'.

The morula reaches the uterine cavity and becomes attached to the inner lining of the uterus (the endometrium) on the 6th day after ovulation. It begins to burrow into the spongy endometrium and by the 10th day, it is completely embedded in it and begins to develop into a baby. The process of embedding into the endometrium is called 'Implantation'.

Please click here to read more about how a pregnancy occurs

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