In a healthy pregnancy your HCG levels should double every 48 hours. But when the pregnancy is not progressing the way it should as in the case of chromosomal abnormality your HCG may rise at slower rates or rise at first and then start to decline. Low HCG levels do not cause miscarriage.
The definition of an invoice is a detailed list of products or services showing the money owed for each item. An example of an invoice is a list of an artist's contributions to a magazine for the month. Invoice is defined as to make or send a list of goods or services for which money is owed. An example of to invoice is to send a bill for written pieces submitted for the week.
late 14c., petition (to God or a god) for aid or comfort; invocation, prayer; also a summoning of evil spirits, from Old French invocacion (12c.), from Latin invocationem (nominative invocatio), noun of action from past participle stem of invocare to call upon, invoke, appeal to (see invoke).