It is quite normal to feel a little dizzy and lightheaded while you are pregnant. Most women experience these symptoms due to the normal body changes occurring during this time . However, in some rare cases they may be associated with serious complications.
Is dizziness an early sign of pregnancy?
It is often considered a symptom of pregnancy occurring early in the first trimester , sometimes even before one notices a missed period, along with other signs like fatigue, nausea and diarrhea. However in many women, dizziness does not occur until the second or even third trimesters .
Causes of Dizziness and Fainting during Pregnancy
The cardiovascular changes are principally responsible for the feeling of lightheadedness  as pregnancy increases the blood volume in your body (by around 50%) to accommodate the needs of the fetus. Additionally, the higher levels of pregnancy hormones cause your blood vessels to dilate, lowering your blood pressure which reaches its lowest point at around mid or late second trimester. The low BP levels often hamper the blood flow to the brain, leaving you dizzy or faint . It may also result from high blood pressure levels towards the last trimester. Expecting twins, having a history of low blood sugar, anemia or diabetes and suffering from varicose vein or gestational diabetes may increase your risks of developing this symptom . The growing uterus, putting pressure on your blood vessels, may lead to dizziness. Additionally, lying on your back in the third trimester makes the baby press on the vena cava (the principal vein carrying blood to the heart from the lower body), making you feel lightheaded.
How to prevent dizziness while pregnant?
- Avoiding standing up too quickly from sitting and lying down positions as this may momentarily deprive your brain of adequate blood supply 
- Including protein-rich foods to every meal for keeping your blood sugar levels stable 
- Eating multiple small meals instead of three large ones as dizziness tends to worsen after eating a large meal or staying without food for extended periods 
- Drinking plenty of fluids to stay hydrated
- Following a diet containing iron-rich foods 
- Carrying some healthy pregnancy snack (whole wheat crackers, raisins, fresh fruits) so you can quickly boost your blood sugar levels whenever the dizzy spells hit 
- Taking your prenatal vitamins and iron supplements (in case you are anemic) regularly 
- Practicing relaxation techniques and yoga to manage stress
- Avoiding over-exercising
- Always lying on your left side to boost blood flow to your heart and brain
- Avoiding going to stuffy congested places
Dizziness in Pregnancy Treatment and Management
It is not always possible to prevent the lightheadedness associated with pregnancy. But, it can be easily managed with certain measures:
- Lying down or sitting down putting your head between the knees (do not put pressure on your belly) 
- Sipping some water
- Loosening any tight clothing (belts, hats or mufflers) to increase blood flow
- Taking slow deep breaths 
- Moving to fresh air
When to call the doctor?
Persistent or recurring dizziness accompanied by one or more of the following symptoms may indicate complications like placental abruption, ectopic pregnancy , pre-term labor and contractions  or miscarriage :
- Severe abdominal pain or cramping
- Pelvic pain
- Blurred vision
- Severe nausea and vomiting 
- Persistent headache
- Vaginal bleeding
- Palpitations 
- Shortness of breath
Dizziness ICD-9 and ICD-10 Codes
The ICD-9 code used for dizziness is 780.4  while its ICD-10 code is R42 [ref]
- http://apps.who.int/classifications/icd10/browse/2010/en#/R42 [/ref]