The placenta is an ephemeral organ formed during the gestation (pregnancy). The placenta develops from the same sperm and egg cells that form the fetus, and functions as a foetomaternal organ with two components.

For nine months the placenta feeds and nourishes the fetus. It receives nutrients, oxygen, antibodies, and hormones from the mother's blood, and disposes toxic waste. It also forms a barrier known as the "placental barrier" and does not allow the mother’s blood to mix with that of the embryo, thus avoiding the possible transfusion of different blood types.

During conception, the placenta implants itself somewhere in your uterus, in no specific position. In a reported 0.5 percent of the pregnancies, the placenta, instead of implanting itself on the uterine wall, it implants partly or wholly over the cervix – the condition known as Placenta Praevia or low-lying placenta.

The placental position can be known in the scan taken at 18-20 week of pregnancy.

Even if reported with a low-lying placenta in the first half of your pregnancy, it is not usually a cause for concern. As the womb gets bigger, the likelihood of placenta moving up, away from the cervix is high.

Conversely, if the placenta fails to move upwards as the pregnancy progresses, is can cause complications.

Warning signs of placenta praevia
Painless vaginal bleeding, ranging from heavy to light, during the last three months of pregnancy. However, there may be no warning signs at all and the fact that you have placenta praevia is actually confirmed during a routine ultrasound scan.

Risk Factors
Although there are no specific causes of placenta previa, there are some factors that may increase your risks for the disorder:
• Cigarette smoking.
• First pregnancy after a cesarean birth.
• Prior placenta previa
• Advanced maternal age
• Women with frequent pregnancy
• Multiple pregnancy
• Prior history of induced abortion
• Sever scarring of the uterus.

Precautions:
• Go in for more trans-vaginal ultrasound scans to check whether the position of the placenta has lifted with the development and stretching of the womb.
• In case you are detected with major placenta praevia (the placenta covers the entrance to the cervix), you may be offered admission to hospital after 34 weeks of pregnancy.
• In case you bleed suddenly and severely, you may need an urgent cesarean section.
• Avoid stimulating the cervix; abstain from sex, vaginal manipulation, and douching.
• Eat a healthy diet rich in iron to reduce the risk of anemia.
• Avoid doing any lifting, strenuous work, or aerobic exercise.