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.
The purpose of an invoice is to create an obligation to make a payment for products or services purchased by a customer, while the presentation of a statement is to provide a summary -- designed to clarify and highlight what is owed by the customer.