This surprises me in light of the facts that you set out. The Texas Medical Board posts information on its website about aspects of this issue, including the rights of patients to access their records, reasonable fees, etc. In pertinent part, the webpage which is linked below, explains "State law [Medical Practice Act, Section 5.08(K)] allows a patient to obtain a copy of his records, or ask that a copy be sent to a new doctor or someone else, such as an insurance company," and, more directly, "Board rule 165.1 defines a reasonable fee to be a charge of no more than $25 for the first twenty pages and $.50 per page for every copy thereafter. For x-rays, $8.00 per film. In addition, a reasonable fee may include actual costs for mailing, shipping, or delivery. The physician shall be entitled to payment of a reasonable fee prior to release of the information unless the information is requested by a licensed Texas health care provider or physician, if requested for purposes of emergency or acute medical care. In the event payment is not included with the request, within ten calendar days from receiving a request for the release of records for reasons other than emergency or acute medical care, the physician shall notify the requesting party in writing of the need for payment and may withhold the information until payment of a reasonable fee is received." Being 30 weeks pregnant probably doesn't qualify as acute medical care or an emergency. Professionals understandably want to be compensated for their services and costs, but it may be worth discussing the situation with your current physician to ensure that s/he has sufficient information about you and your pregnancy to do what is needed to attend to you and your unborn child.
This answer does not, nor is it intended to, create an attorney-client relationship or constitute attorney advertising. Rather, it is offered solely for information purposes. Since the facts of each case are different, it is important to seek out qualified counsel with whom information can be shared and assessed under an attorney-client privilege so that competent and tailored advice can be provided.
In addition to the prior part of the answer, please note that the Texas Administrative Code provision that I hyperlinked states, in relevant part, the following:
(h) Improper Withholding for Past Due Accounts. Medical and/or billing records requested pursuant to a proper request for release may not be withheld from the patient, the patient's authorized agent, or the patient's designated recipient for such records based on a past due account for medical care or treatment previously rendered to the patient.
To the extent that this is the situation, it would appear that a letter which points this provision may resolve the problem.