embro sac and no fetus

I went to the doctor last week and they said It wad to early to tell how far i was in my pregnancy due to me not remembering my last period was. I went back this week and he said that it didn't look good he saw a sac which was to big not to have a fetus but no fetus. He asked me if I wanted to wait another week and I said yes. My concern is i had one miscarraige (miscarriage) about 7yrs ago and I had the same issue with a sac and no embryo a year and a half ago which lead me to have to get an dnc. My ? is how likely is this to happen twice and why does it happen?I have a 9yr old son and had no problems then.

[peekawho]

Once you have had 2 miscarriages, probably effort should be made into investigating possible reasons.  

This is from an ACOG journal about repeated miscarriage:

"Sometimes a miscarriage can be linked to chromosomal problems in the fetus, medical conditions in the woman, or problems with the woman's uterus. There are tests to help your doctor determine what caused the miscarriage and in some cases treatment is available to avoid problems in future pregnancies.

Chromosomal Problems. More than one half of miscarriages in the first 13 weeks of pregnancy are caused by problems with the chromosomes of the fetus. Chromosomes are tiny structures in the cells of the body. Each carries many genes. Genes determine all of a person's physical traits, such as sex, hair and eye color, and blood type.

There can be problems with the number or structure of chromosomes, or with the genes they carry. Extra or missing chromosomes or genes mean the fetus will not grow as it should. Often miscarriage is nature's way of ending a pregnancy in which the fetus would not have been able to live.

Many such problems occur by chance and have nothing to do with the health of the mother or father. However, in a small number of cases, problems with the parents' chromosomes can cause repeated miscarriage. There are tests to find out if such problems are a factor in repeated miscarriage.

Problems of the Uterus. Several problems of the uterus are linked to repeated miscarriage. Most are not common. They include:

Defects present from birth, such as a uterus that is divided into two sections by a wall of tissue (septate uterus).
Benign growths in the uterus, such as fibroids, made up of muscle tissue.
The cervix that begins to widen and open too soon, in the middle of pregnancy, with no sign of pain or labor.
Most of these problems can be treated with surgery. Your doctor will advise you of your options.
Medical Conditions. Certain conditions in the mother have been linked to a greater risk of repeated miscarriage. These include:

Lupus and other autoimmune disorders
Heart disease
Severe kidney disease, mainly when linked with high blood pressure
Diabetes
Thyroid disease
Infection in the uterus
Polycystic ovary syndrome
In some cases, treating the condition can improve the chance of a successful pregnancy. This is even more true if the condition is under control before a woman becomes pregnant.
Antiphospholipid Syndrome. Antiphospholipid syndrome is a disorder of the immune system. Women with antiphospholipid syndrome are at increased risk for blood clots and pregnancy loss. Tests can be done to diagnose this condition.

Possible Factors

There are other factors that are known to cause pregnancy loss. The link between these factors and miscarriage is not clear. The most common ones include hormone imbalance and some blood disorders. If your doctor suspects any of these conditions, he or she may want to do a test and, if necessary, prescribe medication to treat the problem so it does not affect your pregnancy.

Hormone Imbalance. Progesterone is a hormone that prepares the lining of the uterus to nourish a fertilized egg. This happens during the second half of the menstrual cycle. Early in pregnancy, if progesterone levels are too low to maintain the pregnancy, miscarriage can occur. Tests can show if a woman's body is not making enough progesterone. Her doctor may prescribe medication to treat the problem.

Certain Blood Disorders. Thrombophilia is a type of disorder that can make blood clot more than it should. There are several types of genetic disorders that can lead to thrombophilia. One type of disorder, Factor V Leiden mutation, may allow clots to form in the blood vessels to the placenta and lead to miscarriage. Pregnant women with this disorder may be prescribed blood thinners. "